Patent Publication Number: US-2023149697-A1

Title: Variable stiffness cannula

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Provisional Application No. 63/280,209, filed Nov. 17, 2021, which is herein incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to percutaneous circulatory support devices. More specifically, the disclosure relates to percutaneous circulatory support devices having a cannula. 
     BACKGROUND 
     Circulatory support devices support the pumping action of the heart. These devices may be disposed through a valve opening such as, for example, an aortic valve. Blood flow through the circulatory support devices is an important factor when differentiating between different types of circulatory support devices. In some instances, a cannula may be used for providing blood flow through the circulatory support device. Proper positioning and stability of the cannula are important factors for retaining the proper blood flow and function of the circulatory support device. 
     SUMMARY 
     In Example 1, a percutaneous circulatory support device includes a housing, a cannula coupled to the housing, the cannula having a first portion and a second portion. The cannula includes at least one slot disposed along at least the first portion of the cannula, the at least one slot configured such that the first portion of the cannula is defined by a first stiffness and a second portion of the cannula is defined by a second stiffness, the first stiffness being different than the second stiffness. 
     In Example 2, the percutaneous circulatory support device of Example 1 includes wherein the at least one slot is formed by laser cutting. 
     In Example 3, the percutaneous circulatory support device of Example 1, includes wherein the first portion is defined as a distal portion of the cannula and the second position is defined as a proximal portion of the cannula, and the first stiffness is less than the second stiffness. 
     In Example 4, the percutaneous circulatory support device of Example 1, further includes wherein the at least one slot includes a plurality of circular openings extending through the cannula. 
     In Example 5, the percutaneous circulatory support device of Example 1, further includes wherein the at least one slot includes a plurality of slots extending around the cannula. 
     In Example 6, the percutaneous circulatory support device of Example 1, further includes wherein the at least one slot defines a spiral slot extending around and along the cannula. 
     In Example 7, the percutaneous circulatory support device of Example 1, further includes wherein the cannula includes a coating configured to reduce the coefficient of friction of the cannula. 
     In Example 8, the percutaneous circulatory support device of Example 1, further includes wherein the cannula includes a shape set curved portion. 
     In Example 9, the percutaneous circulatory device of Example 3, further includes wherein the distal portion of the cannula includes an atraumatic tip element. 
     In Example 10, a percutaneous circulatory support device includes an impeller disposed within an impeller housing, the impeller being rotatable relative to the impeller housing to cause blood to flow through the impeller housing, and a motor configured to rotatably drive the impeller within the impeller housing. The device additionally includes a cannula coupled to the impeller housing, the cannula having a proximal portion, a distal portion, and an intermediate portion. The device further includes the cannula having at least one slot extending through the cannula and disposed along at least a first portion of the cannula, the at least one slot formed from laser cutting, and the first portion of the cannula body being defined by a first stiffness and a second portion of the cannula body being defined by a second stiffness that is different than the first stiffness. 
     In Example 11, the percutaneous circulatory support device of Example 10 further includes wherein the cannula comprises a curved portion, and wherein the curved portion defines a third portion having a third stiffness. 
     In Example 12, the percutaneous circulatory support device of Example 10 further includes wherein the distal portion of the cannula is operatively coupled to an atraumatic tip. 
     In Example 13, a method of forming a cannula of a percutaneous circulatory device, the percutaneous circulatory device including an impeller disposed within an impeller housing, the impeller being rotatable relative to the impeller housing to cause blood to flow through the percutaneous circulatory support device, wherein the cannula is configured to provide blood flow into the impeller housing, includes providing a cannula composed of a metallic material, the cannula having a distal portion, a proximal portion, an intermediate portion and a cannula lumen, the cannula lumen extending between the distal portion and the proximal portion. The method further includes shape setting the cannula such that the cannula tube comprises a curved portion, and laser cutting the cannula tube to form at least one slot within the tube such that the proximal portion has a first density of the at least one slot at a first portion of the cannula and a second density of the at least one slot at a second portion of the cannula, the first density being different than the second density. 
     In Example 14, the method of Example 13 further includes, wherein the at least one slot includes a plurality of openings extending circumferentially around the cannula. 
     In Example 15, the method of Example 13 further includes wherein the at least one slot includes at least one spiral cut extending along the cannula. 
     In Example 16, a percutaneous circulatory support device includes an impeller disposed within an impeller housing, the impeller being rotatable relative to the impeller housing to cause blood to flow through the impeller housing and a cannula coupled to the impeller housing, the cannula having a first portion and a second portion. The percutaneous circulatory support device additionally includes wherein the cannula includes at least one slot disposed along at least the first portion of the cannula, the at least one slot configured such that the first portion of the cannula body is defined by a first stiffness and a second portion of the cannula is defined by a second stiffness, the first stiffness being different than the second stiffness. 
     In Example 17, the device of Example 16 further includes wherein the first portion is defined as a distal portion and the second portion is defined as a proximal portion, and the first stiffness is less than the second stiffness. 
     In Example 18, the device of Example 16 further includes wherein the at least one slot includes a plurality of openings, and wherein the first portion has a reduced density of the plurality of openings relative to a density of the plurality of openings at the second portion. 
     In Example 19, the device of Example 16 further includes wherein the at least one slot includes a plurality of circular openings extending through the cannula. 
     In Example 20, the device of Example 16 further includes wherein the at least one slot includes a plurality of slots extending around the cannula. 
     In Example 21, the device of Example 16 further includes wherein the at least one slot defines a spiral slot extending around and along the cannula. 
     In Example 22, the device of Example 16 further includes wherein the cannula body comprises a shape set curved portion. 
     In Example 23, the device of Example 16 further includes wherein the distal portion of the cannula comprises an atraumatic tip element. 
     In Example 24, the device of Example 16 further includes wherein the cannula includes a coating configured to reduce the coefficient of friction of the cannula. 
     In Example 25, the device of Example 16 further includes wherein the cannula is composed of one of nitinol, stainless steel, Inconel and MP35N. 
     In Example 26, a percutaneous circulatory support device includes an impeller disposed within an impeller housing, the impeller being rotatable relative to the impeller housing to cause blood to flow through the impeller housing and a motor configured to rotatably drive the impeller within the impeller housing. The percutaneous support device further includes a cannula coupled to the impeller housing, the cannula having a proximal portion, a distal portion, and an intermediate portion, and wherein the cannula includes at least one slot extending through the cannula body disposed along at least the distal portion of the cannula, wherein the at least one slot is formed from laser cutting, the distal portion of the cannula being defined by a first stiffness and the proximal portion of the cannula being defined by a second stiffness that is different than the first stiffness. 
     In Example 27, the device of Example 26 further includes wherein the cannula comprises a curved portion in the intermediate portion, and wherein the intermediate portion defines a third portion having a third stiffness. 
     In Example 28, the device of Example 26 further includes wherein the third stiffness is different than the first stiffness and the second stiffness. 
     In Example 29, the device of Example 26 further includes wherein the distal portion of the cannula is operatively coupled to an atraumatic tip. 
     In Example 30, a method of forming a cannula of a percutaneous circulatory device, the percutaneous circulatory device including an impeller disposed within an impeller housing, the impeller being rotatable relative to the impeller housing to cause blood to flow through the impeller housing, wherein the cannula is configured to provide blood flow into the impeller, includes providing a cannula composed of a metallic material, the cannula having a distal portion, a proximal portion, and a cannula lumen extending between the proximal portion and the distal portion. The method further includes shape setting the cannula such that the cannula tube includes a curved portion and laser cutting the cannula tube to form at least one slot within the cannula such that the proximal portion has a first density of the at least one slot at a first portion of the cannula and a second density of the at least one slot at a second portion of the cannula, the first density being different than the second density. 
     In Example 31, the method of Example 31 further includes attaching a tip element to the distal portion of the cannula. 
     In Example 32, the method of Example 30 further includes wherein the metallic material is one of nitinol, stainless shell, Inconel, and MP35N. 
     In Example 33, the method of Example 30 further includes wherein the at least one slot includes a plurality of openings extending circumferentially around the cannula. 
     In Example 34, the method of Example 30 further includes wherein the at least one slot includes at least one spiral cut extending along the cannula. 
     In Example 35, the method of Example 30 further includes an intermediate portion extending between the proximal portion and the distal portion, and wherein the intermediate portion includes the curved portion. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a conceptual diagram of a circulatory support device including a cannula and a connector, in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  2    is a side sectional view of several components of an illustrative percutaneous circulatory support device, in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  3    is a side view of a cannula of the illustrative percutaneous circulatory support device of  FIG.  2   , in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  4    is a side view of a cannula of the illustrative percutaneous circulatory support device of  FIG.  1   , in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  5    is a side view of a cannula of the illustrative percutaneous circulatory support device of  FIG.  1   , in accordance with embodiments of the subject matter disclosed herein. 
         FIG.  6    illustrates various embodiments of a plurality of openings of a cannula, in accordance with embodiments of the subject matter disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. 
     Embodiments disclosed herein include circulatory support devices that have an increased flow capability in comparison to conventional embodiments. 
       FIG.  1    depicts a conceptual diagram of a circulatory support device  102 , including a cannula  104  and a connector  108 , in accordance with embodiments of the subject matter disclosed herein. The circulatory support device  102  is shown arranged within a heart  110 . According to embodiments, the circulatory support device  102  (also referred to herein, interchangeably, as a “blood pump”) is coupled to the cannula  104  by the connector  108 . The circulator support device  102  is configured to pump blood from the subject&#39;s left ventricle  112  into the subject&#39;s aorta  114 . In embodiments, the circulatory support device  102  may be used to treat cardiogenic shock and other heart failure modalities. 
     In embodiments, a distal portion  116  of the cannula  104  is arranged in the left ventricle  112 . An intermediate portion  118  of the cannula  104  extends through the aortic valve  120  so that a proximal portion  122  of the cannula  104  extends into the aorta  114 . In embodiments, the proximal portion  122  of the cannula  104  is coupled to the connector  108  and the connector  108  is coupled to the circulatory support device  102 . In other embodiments, the cannula  104  is coupled to the circulatory support device without the use of a connector. During operation, the circulatory support device  102  draws blood from the left ventricle  112 , through the cannula  104  of the circulatory support device  102  and is released into the aorta  114 . Additionally, or alternatively, the circulatory support device  102  may be used to facilitate pumping blood from some other aspect of the subject&#39;s vasculature into an adjacent portion of the vasculature. 
       FIG.  1    is not intended to suggest any limitation as to the scope of use or functionality of embodiments of the present disclosure.  FIG.  1    also should not be interpreted as having any dependency or requirement related to any single component or combination of components illustrated therein. Additionally, various components depicted in  FIG.  1    may be, in embodiments, integrated with various ones of the other components depicted therein (and/or components not illustrated), all of which are considered to be within the ambit of the present disclosure. 
       FIG.  2    depicts a partial side sectional view of the circulatory support device  102  depicted in  FIG.  1    and the cannula  104 , in accordance with embodiments of the subject matter disclosed herein. As previously disclosed with reference to  FIG.  1   , the cannula  104  may include a proximal portion  122 , an intermediate portion  118 , and a distal portion  116 . The proximal portion  122  is positioned coupled to the connector  108  which is then operatively coupled to the remainder of the circulatory support device  102 , the components of which will be described further herein. 
     Further, as illustrated, the cannula  104  may comprise a tip element  154  attached to the distal portion  116  of the cannula  104 . As illustrated, the tip element  154  is a spherical element that is coupled to the distal portion  116  through the use of a plurality of wires  158 . Specifically, the plurality of wires  158  are coupled to the distal portion  116  of the cannula  104  and coupled directly to the tip element  154 . The tip element  154  may prevent suction of tissue into the cannula  104  by spacing the distal portion  116  away from tissue. While illustrated as a sphere, the tip element  154  may be any variety of shapes, for example a rectangle or a cylinder. Additionally, or alternatively, the tip element  154  may be radiopaque to help determine proper positioning of the cannula  104  during or after delivery. Further, the spaces between the plurality of wires  158  may act as an inlet for the blood to enter the cannula  104 . In other embodiments, an inlet may be defined by other features, such as a housing coupling the intermediate portion  118  of the cannula  104  to the tip element  154 . Additionally, or alternatively, tip element  154  acts as an atraumatic tip element configured to protect the patient&#39;s vasculature or the tissue of the heart  110 , including valvular tissue, by eliminating harsh edges or surfaces that could come into contact with the surrounding vasculature or tissue as the cannula  104  is navigated to, into, or through the heart  110 . For example, the tip element  154  may include a solder ring, a balloon and/or a silicone ring to serve as an atraumatic tip element. Further, in other embodiments, an elongated tip, for example taking shape similar to a guidewire, is used as the tip element  154 . In some embodiments, no tip element is incorporated with the cannula  104  at all. 
     With continued reference to  FIG.  2   , the circulatory support device  102  generally includes an impeller housing  130  and a motor housing  132 . In some embodiments, the impeller housing  130  and the motor housing  132  may be integrally or monolithically constructed. In other embodiments, the impeller housing  130  and the motor housing  132  may be separate components configured to be removably or permanently coupled. 
     The impeller housing  130  carries an impeller assembly  134  therein. The impeller assembly  134  includes an impeller shaft  136  that is rotatably supported by at least one bearing, such as a bearing  138 . The impeller assembly  134  also includes an impeller  140  that rotates relative to the impeller housing  130  to drive blood through the device  102 . More specifically, the impeller  140  causes blood to flow from a blood inlet  142  formed on the impeller housing  130 , through the impeller housing  130 , and out of a blood outlet  144  formed on the impeller housing  130 . In some embodiments and as illustrated, the impeller shaft  136  and the impeller  140  may be separate components, and in other embodiments the impeller shaft  136  and the impeller  140  may be integrated. In some embodiment and as illustrated, the inlet  142  and/or the outlet  144  may each include multiple apertures. In other embodiments, the inlet  142  and/or the outlet  144  may each include a single aperture. In some embodiments and as illustrated, the inlet  142  may be formed on an end portion of the impeller housing  130  and the outlet  144  may be formed on a side portion of the impeller housing  130 . In other embodiments, the inlet  142  and/or the outlet  144  may be formed on other portions of the impeller housing  130 . As illustrated and previously described, the impeller housing  130  couples to the cannula  104  such that the cannula  104  receives and delivers blood to the blood inlet  142 . 
     With continued reference to  FIG.  2   , the motor housing  132  carries a motor  146 , and the motor  146  is configured to rotatably drive the impeller  140  relative to the impeller housing  130 . In the illustrated embodiment, the motor  146  rotates a drive shaft  148 , which is coupled to a driving magnet  150 . Rotation of the driving magnet  150  causes rotation of a driven magnet  152 . The driven magnet  152  is connected to and rotates together with the impeller assembly  134 . More specifically, in embodiments incorporating the impeller shaft  136 , the impeller shaft  136  and the impeller  140  are configured to rotate with the driven magnet  152 . In other embodiments, the motor  146  may couple to the impeller assembly  134  via other components. 
     In some embodiments, a controller (not shown) may be operably coupled to the motor  146  and configured to control the motor  146 . In some embodiments, the controller may be disposed within the motor housing  132 . In other embodiments, the controller may be disposed outside of the motor housing  132  (for example, in a catheter handle, an independent housing, etc.). However, the above described embodiment of the circulatory support device  102  is not meant to be limiting and the cannula  104 , and any variations of the cannula described herein with reference to  FIGS.  1 - 6   , may be used with variations of other circulatory support devices. Even further, the cannula  104  described herein may be used with various other percutaneous devices. The cannula  104 , and various embodiments thereof, will be described further herein. 
       FIG.  3    illustrates an embodiment of a cannula  204  that may be used in combination with the circulatory support device of  FIG.  1   . Similar to the cannula  104  of  FIG.  1   , the cannula  204  comprises a proximal portion  222 , an intermediate portion  218 , and a distal portion  216 . Additionally, the cannula  204  comprises a curved portion  228  within the intermediate portion  218 . In some embodiments, the cannula  204  includes a plurality of curved portions at different positions along the cannula  204 . The cannula  204  comprises a cannula body  224  and a lumen  226  extending between the proximal portion  222  and the distal portion  216 . The lumen  226  is configured for the passage of blood into the cannula  204  and into the blood inlet  142  ( FIG.  2   ) of the device  102  ( FIG.  1   ). As shown, the cannula lumen  226  is generally cylindrical in shape, however, various other shapes and configurations may be incorporated. The cannula  204  may be formed from a variety of materials. For example, the cannula  204  may be composed of materials including, but not limited to, nitinol, stainless steel, Inconel, and MP35N. The use of the above present materials, or various other appliable materials, allows for the cannula  204  to be shape set into a desired shape or configuration, as well as the ability for the cannula  204  to be laser cut or otherwise altered to have slots. For example, the cannula  204  may be formed by cutting slots into a hypo tube formed of any one of the above materials, as will be described further herein. 
     As shown in  FIG.  3   , the cannula  204  includes the curved portion  228  that is positioned adjacent the proximal portion  222  of the cannula  204  and within the intermediate portion  218  of the cannula  204 . However, the positioning of the curved portion  228  may vary, for example it may be adjacent the distal portion  216  of the cannula  204 . The curved portion  228  may be formed by shape setting the cannula  204 , for example with a heat set. The configuration of the curved portion  228  of  FIG.  3    is not meant to be limiting, and may comprise a radius of curvature that is greater than, equal to, or less than the radius of curvature shown in  FIG.  3   . In various embodiments, the curved portion  228  may provide at least the advantage of optimized shaping of the cannula  204  relative to the native anatomy of the heart  110  ( FIG.  1   ) when in use with the device  102  ( FIG.  1   ). For example, when the cannula  204  is positioned within the heart  110 , the curved portion  228  may be positioned just within the aorta  114  to provide a better positioning of the cannula  204  within the heart  110 , for example with respect to the aortic valve and ventricular walls. In other embodiments, the curved portion  228  may be positioned just above or below the aorta  114 . An additional advantage of the curved portion  228  may be allowing for an easier delivery of the cannula  204  into the heart  110 , as the curved portion  228  may align with the curvature of the chambers in the heart  110 . 
     The shape of the cannula  204  may also be manipulated by hand, for example by a physician adjusting the shape of the cannula  204  prior to insertion into a patient. For example, the curved portion  228  may be formed by a physician prior to the cannula  204  being inserted into a patient&#39;s vasculature. 
     As previously mentioned, an additional advantage of the cannula  204  as disclosed herein, is the ability for slots to be cut into the cannula  204 , for example by laser cutting the cannula  204 . For example, as illustrated in  FIG.  3   , the cannula  204  comprises at least one slot disposed along the cannula  204 . In the embodiment of  FIG.  3   , the at least one slot comprises a plurality of slots  230  extending circumferentially around the cannula  204 . As will be described further with reference to  FIGS.  4 - 5   , the plurality of slots  230  may take various other forms or shapes. With continued reference to  FIG.  3   , each of the plurality of slots  230  extends through the cannula  204  such that it forms an opening extending from an exterior of the cannula  204  to the cannula lumen  226 . However, in various other embodiments, the plurality of slots  230  may extend through only a portion of the cannula  204  such that the plurality of slots  230  extend a depth that is less than a thickness of the cannula  204 . Stated differently, in some embodiments, the slots  230  may not form apertures in the cannula  204 , but instead form areas of reduced thickness of the cannula  204 . 
     The distribution of the plurality of slots  230  may be varied as well. For example, as illustrated in the embodiment of  FIG.  3   , the plurality of slots  230  have a higher density towards the proximal portion  222  and the distal portion  216  relative to the density of the plurality of slots  230  at the curved portion  228  and the intermediate portion  218  of the cannula  204 . Additionally, the density of the plurality of slots  230  may be higher at the distal portion  216  than at the proximal portion  222 . The density may be defined as the amount of open surface area within a given section of the cannula  204  relative to the amount of cannula material, for example nitinol, within the same given section of the cannula  204 . 
     One advantage of the incorporation of the plurality of slots  230 , and particularly with varying density along the cannula  204 , allows for the cannula  204  to have a varying stiffness and/or varying amounts of flexibility throughout the cannula  204  while maintaining a constant wall thickness. For example, the distal portion  216  may be formed with a higher plurality of slots  230  in order to increase the flexibility at the distal portion  216  of the cannula  204 . In this way, the cannula  204  is still capable of flexibility and a range of motion at the distal portion  216 . Further, the cannula  204  may have a lower density of the plurality of slots  230  towards the curved portion  228  to increase the stiffness of the curved portion of the cannula  204 . This may provide the advantage of increasing the stability of the curved portion  228  when it is positioned at the aorta  114  ( FIG.  1   ) and increasing the trackability of the cannula  204 . Further, in various embodiments, the plurality of slots  230  may have a higher density at the proximal portion  222  to increase the flexibility relative to the flexibility of the curved portion  228 . In other embodiments, the plurality of slots  230  may have a lower density in the proximal portion  222  than the curved portion  228  to increase the flexibility of the curved portion  228  relative to the proximal portion  222 . In this way, the stiffness of the various portions of the cannula  204  may easily be varied based on the amount of the plurality of slots  230  incorporated. In additional embodiments, the arclength of the material between the plurality of slots  230  of the cannula  204  may contribute to the varying stiffness values along the cannula  204  as well. In some embodiments, the stiffness at the proximal portion  222  is adjusted to match the stiffness of the component that the proximal portion  222  is attached to in assembly, such that there is a smooth transition between the stiffness of the cannula  204  and the adjacent component, for example, the connector  108  ( FIG.  1   ). The above described relative stiffnesses are not meant to be limiting, and the at least one slot of the cannula  204  may be varied and distributed to best optimize the trackability and flexibility of the cannula  204 . For example, the cannula  204  could comprise a continuously changing stiffness profile based on the configuration of the plurality of slots  230  to optimize the stiffness transition throughout the cannula  204 . For example, the continuously changing stiffness profile could be defined by linear, parabolic, and/or polynomial curves to optimize the stiffness transitions. 
     Additionally, between each portion of the cannula  204  that defines varying stiffness values, the plurality of slots  230  may be configured to provide gradual increases (or decreases) in the stiffnesses. Incorporating gradual transition between the varying stiffness values may increase the stability of the cannula  204  as opposed to if abrupt changes in the stiffness were present. Varying the stiffness and/or varying the amounts of flexibility throughout the cannula  204  may also permit manipulation of the cannula  204  by the physician before or after insertion into the vasculature, as described above. For example, the pattern of the slots  230  may be designed to control the bending amount or direction of the cannula  204 . 
     An additional advantage of using the plurality of slots  230  is the ability to optimize the insertion of the cannula  204  through the vasculature and into the heart  110  ( FIG.  1   ). In particular, cannula  204  allows for delivery of a circulatory support device without the use of a guidewire. For example, the stiffness along the cannula  204  can be optimized such that the cannula  204  is flexible enough to be navigated and moved into the target position without damaging the tissue, yet stable enough to be passed through the patient&#39;s vasculature and the heart  110  and positioned properly and held in position within the heart  110 . In other words, the cannula  204  needs to be flexible enough to maneuver through the curvature of the vascular system, but stable enough not to fold on itself or collapse while passing through the vascular system and into the heart. Thus, while a guidewire (not shown) may be incorporated to deliver the circulatory support device  102  to the target position, the optimized stiffness of the cannula  204  through incorporation of the plurality of slots  230  allows the cannula  204  to be delivered through the heart  110  without the use of a guidewire. 
     An additional feature that may be incorporated into the cannula  204  is a surface coating  240  disposed around the entirety of the cannula  204 . In some embodiments, the surface coating  240  is a silicone, PET, or other biocompatible and/or hydrophobic polymers such as polyether block amide, polytetrafluoroethylene, fluorinated ethylene propylene, or polyurethane. In some embodiments, the surface coating  240  can be hydrophilic. The surface coating  240  may be applied via a dip coating, a spray coating, molding, heat shrink, or polymer reflow process among other methods. The surface coating  240  may be attached to the cannula body  224 , and thus the cannula  204 . The surface coating  240  may be provided for optimizing the cannula  204  for trackability and biocompatibility. For example, the surface coating  240  may reduce the coefficient of friction of the cannula  204  to increase the ease with which the cannula  204  is delivered into the heart  110 . Additionally, the use of the surface coating  240  increases the biocompatibility of the cannula  204  to avoid undesired reactions between the cannula  204  and tissue of the vasculature. Further, the surface coating  240  may be applied such that the entirety of the outer surface and the inner surface of the cannula  204  is covered. In the embodiments wherein the plurality of slots  230  are a plurality of apertures extending entirely through the cannula  204 , the surface coating  240  creates a seal over the plurality of slots  230  such that the cannula  204  is a sealed tube and does not allow for fluid or blood flow through the plurality of slots  230 . Even further, the cannula  204  may comprise an additional surface coating  242  on an inner surface the cannula  204 . Similar to the surface coating  240  as described with reference to  FIG.  2   , the surface coating  240  may be a silicone, PET or other polymer coating. The surface coatings  240 ,  242  may be applied to the embodiments of any one of  FIGS.  1 - 5    herein, and are not limited to the use with the cannula  204  of  FIG.  3   . 
       FIG.  4    illustrates an additional embodiment of a cannula of the device  102  as described previously with reference to  FIG.  1   . Specifically,  FIG.  4    is a side view of a cannula  304 . The cannula  304  may be largely similar to the cannula  204  as described with reference to  FIG.  3   . For example, the cannula  304  comprises a distal portion  316 , a curved portion  328  within an intermediate portion  318 , and a proximal portion  322 . The cannula  304  additionally comprises a cannula body  324  extending between the distal portion  316  and the proximal portion  322 . However, the cannula  304  differs from cannula  204  in that the cannula  304  includes at least one slot that is different than the at least one slot  230  ( FIG.  3   ). Specifically, the at least one slot includes a spiral cut  330  that extends around the cannula  304 . As such, the cannula  304  comprises the spiral cut  330  extending at a diagonal and extending between the distal portion  316  and the proximal portion  322 . The density of the spiral cut  330  along the cannula  304  may vary in density based on a distance between the circumferential segments of the spiral cut  330 . In this way, the stiffness values of the cannula  304  can vary along the cannula  304  for providing the optimized delivery and anchoring of the cannula  304 . 
     While the at least one slot described with reference to  FIGS.  3  and  4    are illustrated generally as slots or thin cuts through the cannula  204 ,  304 , at least one opening of a cannula may vary further in shape or configuration. For example,  FIG.  5    illustrates an additional embodiment of a cannula  404 . Similar to described herein, the cannula  404  includes a distal portion  416 , a curved portion  428  within an intermediate portion  418 , and a proximal portion  422 . The cannula  404  comprises a cannula body  424  extending between the distal portion  416  and the proximal portion  422 . Further, the cannula  404  comprises at least one slot. In this embodiment, the at least one slot comprises a plurality of openings  430  that are illustrated as generally circular holes extending through and along the cannula  404 . However, the plurality of openings  430  may take on any desired shape or pattern. For example, the shape of the plurality of openings  430  may be shaped as a circle, oval, square, rectangle, or any other shape desired. For example, the openings  430  may have a shape that is a combination of the above, for example a dog bone shape defined by a cylinder joined with a circle at each end. Other examples of shapes and/or patterns that may define the plurality of openings  430  are included in  FIG.  6   . For example,  FIG.  6    illustrates a plurality of openings  430   a  having a general dog bone shape. Additionally,  FIG.  6    illustrates a plurality of openings  430   b  having generally rectangular openings disposed along the cannula  404  ( FIG.  5   ) with a pattern. Further,  FIG.  6    illustrates an additional configuration of the plurality of openings, illustratively a plurality of openings  430   c  that are generally rectangular or ovular slots that extend adjacent one another along the cannula  404 . Further, the plurality of openings  430   d  illustrate a pattern of both circumferentially extending slots and longitudinally extending slots to form a pattern of the plurality of openings  430   d  within the cannula  404 . However, the various shapes and patterns illustrated in  FIG.  6    are not meant to be limiting, and various other shapes and/or patterns of the plurality of openings  430  may be incorporated. The plurality of openings  430  function similarly to the at least one slot  230  as described with reference to  FIG.  3    and the spiral cut  330  as described with reference to  FIG.  4   , wherein the positioning and density of the openings  430  along the cannula  404  allows for a varied stiffness along the cannula  404 . 
     While the following description is made with reference to the cannula  404  illustrated in  FIG.  5   , the following description applies to cannulas  104 ,  204 , and  304  as described with reference to  FIGS.  1 - 4   . The plurality of openings  430  may be formed through laser cutting the cannula  404  or otherwise machining the cannula  404 . In addition, in the embodiments wherein the cannula  404  is laser cut, additional surface features may be incorporated onto the cannula  404 . For example, as illustrated in  FIG.  5    the cannula  404  additionally includes surface features  440 . Specifically, surface features  440  may be echogenic surface features  440  that are formed directly onto the cannula  404 . This may be particularly advantageous in that after the cannula  404  and the circulatory support device  102  ( FIG.  1   ) are positioned in the heart  110  ( FIG.  1   ), a physician may conduct an imaging test, for example an ultrasound, of the heart  110  of the patient that reveals the positioning of the cannula  404  and the circulatory support device  102 . The surface features  440  may comprise at least one surface feature  440 , however various other amounts of surface features or markings can be imagined. For example, the cannula  404  can comprise two, three, four, five, or more surface features for indicating the position. For example, the cannula  404  may have a first surface feature  440   a  positioned at the distal portion  416  of the cannula  404  and/or a second surface feature  440   b  at the proximal portion  422  of the cannula  404 . This may indicate to the physician the physical bounds of the cannula  404  once positioned. Further, the surface features  440  may include a third surface feature  440   c  positioned at a curved portion  428  of the cannula  404 . As such, in embodiments wherein the curved portion  428  is positioned at or approximately at the aorta  114  ( FIG.  1   ) of the heart  110  ( FIG.  1   ), the physician can be indicated when the curved portion  428  is positioned at the aorta  114  ( FIG.  1   ). The surface features  440  may comprise at least one, all, or any combination of the described surface features  440 . 
     The described features of the cannulas  104 ,  204 , and  404  are not meant to be limited to their embodiments. For example, various features as described with reference to cannula  204  may be used in combination with the cannula  404  or the cannula  104 . For example, the tip element  154  may be incorporated into cannula  204  and/or cannula  304  and/or cannula  404  as well. Further, the surface coating  240  as described with reference to the cannula  204  may be used in combination with the cannulas  104 ,  304 , and/or  404  as described with reference to  FIGS.  1 - 2  and  4 - 5   . Further, the surface features  440  as described with reference to the cannula  404  of  FIG.  5    may be used in combination with the cannulas  104 ,  204 ,  304  as described with reference to  FIGS.  1 - 4   . 
     Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.