Abstract:
A cannula is provided with one or more pressure transducers for measuring fluid pressure interiorly or exteriorly of the cannula. The pressure transducers may be mounted integrally with the tubular wall defining the main lumen of the cannula, or they may comprise differential pressure transducers mounted in dedicated lumens in communication with the main lumen. The pressure measurements from the transducers is used to determine fluid flow rate.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of co-pending U.S. patent application Ser. No. 15/239,697, filed Aug. 17, 2016, which is a divisional of co-pending U.S. patent application Ser. No. 15/239,574, filed Aug. 17, 2016, which is a divisional of co-pending U.S. patent application Ser. No. 14/966,669, filed Dec. 11, 2015, which is a divisional of U.S. patent application Ser. No. 14/543,815, filed Nov. 17, 2014 (now U.S. Pat. No. 9,327,068, issued May 3, 2016), which is a continuation of U.S. patent application Ser. No. 12/772,810, filed May 3, 2010 (now U.S. Pat. No. 8,888,728, issued Nov. 18, 2014), which is a continuation of U.S. patent application Ser. No. 11/375,926, filed Mar. 15, 2006 (now U.S. Pat. No. 7,731,675, issued Jun. 8, 2010), which is a divisional of U.S. patent application Ser. No. 10/070,178, filed Jul. 19, 2002, (now U.S. Pat. No. 7,022,100, issued Apr. 4, 2006) which claims the benefit of PCT/US00/24515 filed Sep. 1, 2000, which claims the benefit of provisional U.S. Patent Application Ser. No. 60/152,249 filed Sep. 3, 1999. We hereby claim priority to the aforementioned application(s) and also incorporate herein by reference each of the afore-listed patents and applications in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to blood pumps and, more particularly, to an improved intra-vascular blood pump having a guide mechanism which provides the ability to selectively guide the intravascular pump to a desired location within a patient&#39;s circulatory system. 
       DESCRIPTION OF RELATED ART 
       [0003]    Over the years, various types of blood pumps have been developed for the purpose of augmenting or replacing the blood pumping action of damaged or diseased hearts. Blood pumps are commonly used in three situations: (1) for acute support during cardio-pulmonary operations; (2) for short-term support while awaiting recovery of the heart from surgery; or (3) as a bridge to keep a patient alive while awaiting heart transplantation. The pumps may be designed to provide right and/or left ventricular assist, although left ventricle assist is the most common application in that it is far more common for the left ventricle to become diseased or damaged than it is for the right ventricle. 
         [0004]    Blood pumps must provide leak-free operation and must avoid contamination of the fluid by the pump components and the external environment. Such pumps must also pump the fluid at a suitable rate without applying excessive Reynolds shear stress to the fluid. It is well known to those skilled in the art that lysis or cell destruction may result from application of shear stress to cell membranes. Red blood cells are particularly susceptible to shear stress damage as their cell membranes do not include a reinforcing cytoskeleton to maintain cell shape. Lysis of white blood cells and platelets also occurs upon application of high shear stress. Lysis of red blood cells can result in release of cell contents which trigger subsequent platelet aggregation. Sublytic shear stress leads to cellular alterations and direct activation and aggregation of platelets and white blood cells. 
         [0005]    Intravascular blood pumps comprise miniaturized blood pumps capable of being percutaneously or surgically introduced into the vascular system of a patient, typically to provide left and/or right heart support. One type of intravascular pump is an axial flow blood pump comprising a cable-mounted rotor surrounded by a protective shroud. The pump, along with the rotor and shroud, are mounted at the end of an elongated flexible catheter. The catheter is inserted into the aorta from a remote entry point, such as an incision below the groin that provides access into a femoral artery. The catheter then passes through the descending aorta until it reaches the ascending aorta, near the heart. The catheter device encloses a rotating drive cable which is coupled to the impeller blade at one end, and which emerges from the exposed end of the catheter, near the patient&#39;s groin, at the other end. When the exposed end of the drive cable is mechanically rotated, using a device located outside the patient&#39;s body, it conveys the rotational force through the length of the catheter, causing the impeller to spin at high speed near the heart. This type of blood pump finds particular application in providing ventricular assist during surgery or providing temporary bridging support to help a patient survive a crisis. 
         [0006]    While generally effective in providing ventricular assisting functions, prior art intravascular blood pumps nonetheless suffer various drawbacks. A significant drawback is that prior art intravascular blood pumps are difficult to guide into the appropriate position within the circulatory system of a patient. This is due largely to the fact that the elongated catheter is incapable of providing the degree of control necessary to easily negotiate the pump through the tortuous pathways leading up to and into the heart. When attempting to place the blood pump in a trans-valvular configuration (with the inlet in the left ventricle and the pump outlet in the ascending aorta), the natural tendency of the catheter to stay straight may cause the pump to be inadvertently placed in the carotid ostia, which can be dangerous if the pump is operated to withdraw blood from the brain. 
         [0007]    To overcome these difficulties, certain guide mechanisms may be employed to assist the physician placing the pump in the appropriate position within the circulatory system. One type of supplemental guide mechanism is a guide catheter. Guide catheters are designed with certain guidability characteristics such that physicians can selectively position them within the vasculature or heart with relative ease. A central lumen is provided within the guide catheter such that the intravascular pump may be introduced therein and guided while it is advanced towards the predetermined circulatory site. While generally effective at providing a guiding feature for such intravascular blood pumps, employing such supplemental guide mechanisms is nonetheless disadvantageous in that they consume valuable space within the vessels. A guide catheter, for example, would necessarily be larger in diameter than the diameter of the pump and protective shroud in order to provide adequate passage of those components. As will be appreciated, this restricts the amount of space available for blood to flow within the particular vessel, and increases the size of the required puncture wound for accessing the vessel. 
         [0008]    The present invention is directed at eliminating and/or reducing the effects of the foregoing drawbacks of prior art intravascular blood pumps. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention overcomes the drawbacks of the prior art by providing an improved intravascular blood pump equipped with integrated features for selectively guiding the intravascular blood pump to a predetermined location in the patient&#39;s circulatory system, i.e. heart and/or vasculature. In so doing, the intravascular blood pump of the present invention eliminates the need for supplemental guiding mechanisms, such as a separate, large diameter guide catheter as used in the prior art. 
         [0010]    In a first broad aspect of the present invention, an intravascular blood pump system is provided comprising an intravascular blood pump having a cannula coupled thereto and an “over-the-wire” type guide mechanism for selectively positioning the intravascular blood pump and cannula at a predetermined location within the circulatory system of a patient. To accomplish this, a central lumen is formed through at least a portion of the intravascular blood pump system such that a guide element, such as a guide wire, may be progressed therethrough and advanced to the predetermined location in the circulatory system of the patient. After the guide element is advanced to this desired location, the intravascular blood pump and cannula may thereafter be advanced along the guide element to the desired location. 
         [0011]    In a second broad aspect of the present invention, an intravascular blood pump system is provided comprising an intravascular blood pump having a cannula coupled thereto and a “side-rigger” or “rapid exchange” type guide mechanism for selectively positioning the intravascular blood pump and cannula at a predetermined location within the circulatory system of a patient. To accomplish this, a side lumen is formed along a length of at least one of the intravascular blood pump and the cannula. A guide element, such as a guide wire, may be advanced to the predetermined location in the circulatory system of the patient. After the guide element is advanced to this desired location, the intravascular blood pump and cannula may thereafter be advanced along the guide element to the desired location. 
         [0012]    In a third broad aspect of the present invention, an intravascular blood pump system is provided comprising an intravascular blood pump having a cannula coupled thereto and a “guide catheter” type guide mechanism for selectively positioning the intravascular blood pump and cannula at a predetermined location within the circulatory system of a patient. The pump system of this broad aspect includes a conduit assembly and a separate pump assembly. The conduit assembly includes a guide catheter, a rotor shroud, and a cannula, with the cannula and guide catheter disposed on either side of the rotor shroud. The pump assembly includes a rotor, a drive member coupled to the rotor, and a pump disposed between the rotor and the drive member. The guide catheter is dimensioned to receive and guide the pump assembly to the point where the rotor docks within the rotor shroud so as to form an operational blood pump. This configuration allows the conduit assembly to be precisely and efficiently guided into a desired position within the body through the use of conventional guiding techniques well known in interventional cardiology. The pump assembly may thereafter be introduced into and guided within the conduit until the pump assembly is docked within the rotor shroud. This dual construction arrangement provides improved placement of the pump assembly by using the conduit as a guiding mechanism. 
         [0013]    The foregoing broad aspects of the present invention may be manifested according to the following recitations: 
         [0014]    According to a first broad recitation of the present invention, an intravascular blood pump system is provided comprising an intravascular blood pump having a cannula coupled thereto, and a guide mechanism adapted to guide the intravascular blood pump and cannula to a predetermined location within the circulatory system of a patient. 
         [0015]    In a further embodiment, the intravascular blood pump includes a rotor, a shroud for receiving the rotor, and a drive cable coupled to the rotor for driving the rotor within the shroud. 
         [0016]    In a further embodiment, the cannula is coupled to the shroud of the intravascular blood pump. 
         [0017]    In a further embodiment, the guide mechanism comprises a guide catheter coupled to the shroud. 
         [0018]    In a further embodiment, the guide catheter may be used to guide the shroud and cannula to the predetermined location within the circulatory system of the patient, after which point the rotor and drive cable of the intravascular blood pump may be docked within the shroud for pump operation. 
         [0019]    In a further embodiment, the drive cable sheath is provided having a central lumen for receiving the drive cable, and wherein a purge fluid delivery system is coupled to the drive cable sheath to deliver purge fluid to the rotor. 
         [0020]    In a further embodiment, the drive cable sheath includes at least one side lumen for delivering the purge fluid towards the rotor. 
         [0021]    In a further embodiment, a portion of the purge fluid is delivered through the at least one side lumen and past the rotor, and a portion of purge fluid is rerouted back from the rotor through the central lumen of the drive cable. 
         [0022]    In a further embodiment, a perfusion assembly is provided communicatively coupled to the guide catheter for selectively rerouting blood from within the guide catheter to a point downstream from the introduction site of the guide catheter into the vasculature of the patient. 
         [0023]    In a further embodiment, the perfusion assembly includes a first conduit communicatively coupled to the guide catheter, a second conduit dimensioned to be introduced into the vasculature of the patient, and a selectively operable valve disposed in between the first conduit and the second conduit. 
         [0024]    In a further embodiment, a blood pressure detection mechanism is provided to detect the pressure of the blood proximate at least one of the intravascular blood pump and cannula. 
         [0025]    In a further embodiment, the blood pressure detection mechanism comprises at least one of fluid filled column disposed within at least a portion of the cannula, a piezoelectric element coupled to at least one of the intravascular blood pump and cannula, and a strain gauge coupled to at least one of the intravascular blood pump and cannula. 
         [0026]    In a further embodiment, the blood pressure detection mechanism involves calculating blood pressure based on the relationship between the torque and motor current of a motor used to drive the rotor. 
         [0027]    In a further embodiment, the guide mechanism comprises a guide element disposed at least partially within the cannula. 
         [0028]    In a further embodiment, the guide element comprises a guide wire for passage through a side lumen formed in the cannula. 
         [0029]    In a further embodiment, the guide element comprises a selectively deformable element disposed at least partially within the cannula. 
         [0030]    In a further embodiment, the intravascular blood pump and cannula may be selectively advanced to the predetermined location within the vasculature of the patient by first passing the guide wire to the predetermined location and thereafter sliding the intravascular blood pump and cannula along the guide wire to the predetermined location. 
         [0031]    In a further embodiment, the guide element comprises a guide wire for passage through a lumen extending through the drive cable and rotor. 
         [0032]    In a further embodiment, the intravascular blood-pump and cannula may be selectively advanced to the predetermined location within the vasculature of the patient by first passing the guide wire to the predetermined location and thereafter sliding the intravascular blood pump and cannula along the guide wire to the predetermine location. 
         [0033]    In a further embodiment, the guide mechanism further includes guide element for passage through the guide catheter to facilitate placement of the shroud and the cannula at the predetermined location within the vasculature of the patient. 
         [0034]    In a further embodiment, the guide mechanism further includes a guide element for passage through a side lumen formed along at least a portion of the guide catheter. 
         [0035]    In a further embodiment, the guide element comprises at least one of a guide wire and a balloon catheter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]    Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein: 
           [0037]      FIG. 1  is a partial sectional view of a human heart illustrating an intravascular blood pump system having an “over-the-wire” type guide mechanism according to a first broad aspect of the present invention positioned, by way of example, in a trans-valvular configuration to provide left-heart assist; 
           [0038]      FIG. 2  is side view of the guidable intravascular blood pump system of the type shown in  FIG. 1  including a motor coupler and purge fluid delivery system according to an exemplary embodiment of the present invention; 
           [0039]      FIG. 3  is a cross-sectional view illustrating an exemplary construction of the blood pump, drive cable assembly, and cannula of the intravascular blood pump system according to the first broad aspect of the present invention; 
           [0040]      FIG. 4  is a cross-sectional view taken along lines  4 - 4  of  FIG. 3  illustrating an exemplary construction of the drive cable assembly and guide mechanism according to the first broad aspect of the present invention; 
           [0041]      FIG. 5  is a cross-sectional view illustrating an exemplary construction of the motor coupler and purge fluid delivery system according to the first broad aspect of the present invention; 
           [0042]      FIG. 6  is a partial sectional view of a human heart illustrating an intravascular blood pump system having a “rapid exchange” or “side-rigger” type guide mechanism according to a second broad aspect of the present invention positioned, by way of example, in a trans-valvular configuration to provide left-heart assist; 
           [0043]      FIG. 7  is side view of the guidable intravascular blood pump system of the type shown in  FIG. 6  including a motor coupler and purge fluid delivery system according to an exemplary embodiment of the present invention; 
           [0044]      FIG. 8  is a cross-sectional view taken along lines  8 - 8  of  FIG. 7  illustrating the “side-rigger” or “rapid exchange” type guide mechanism according to the second broad aspect of the present invention; 
           [0045]      FIG. 9  is a cross-sectional view of the type shown in  FIG. 8  illustrating an alternate configuration of the guide mechanism according to the second broad aspect of the present invention; 
           [0046]      FIG. 10  is a partial sectional view of a human heart illustrating an intravascular blood pump system having a “guide catheter” type guide mechanism according to a third broad aspect of the present invention positioned, by way of example, in a trans-valvular configuration to provide left-heart assist; 
           [0047]      FIG. 11  is a schematic view of a human being illustrating the intravascular blood pump system of the type shown in  FIG. 10  inserted through the femoral artery and including an optional perfusion assembly for perfusing the vasculature downstream from the incision site where guide catheter enters the femoral artery; 
           [0048]      FIG. 12  is a side view of the intravascular blood pump system shown in  FIGS. 10-11  illustrating the separable nature of a pump assembly and a conduit assembly which collectively form the intravascular blood pump system according to the third broad aspect of the present invention; 
           [0049]      FIG. 13  is a side view illustrating the intravascular blood pump system shown in  FIG. 12  with the pump assembly docked into the conduit assembly according to the third broad aspect of the present invention; 
           [0050]      FIG. 14  is a cross-sectional view illustrating an exemplary construction of the blood pump, drive cable assembly, cannula, and guide catheter of the intravascular blood pump system shown in  FIG. 13 ; 
           [0051]      FIG. 15  is a cross-sectional view taken along lines  15 - 15  of  FIG. 14  illustrating an exemplary construction of the drive cable assembly and guide catheter according to the third broad aspect of the present invention; 
           [0052]      FIG. 16  is a cross-sectional view illustrating an exemplary construction of the motor coupler, purge fluid delivery system, and a proximal portion of the guide catheter biasing assembly according to the third broad aspect of the present invention; 
           [0053]      FIG. 17  is a cross-sectional view illustrating an exemplary construction of the perfusion assembly and a distal portion of the guide catheter biasing assembly according to the third broad aspect of the present invention; 
           [0054]      FIG. 18  is a cross-sectional view of an intravascular blood pump system of the type shown in  FIGS. 12-13  having an alternate configuration for docking the rotor within the shroud according to the principles of the present invention; and 
           [0055]      FIG. 19  is a partial sectional view of a human heart illustrating an alternate intravascular blood pump system having an “over-the-wire” type guide mechanism according to the first broad aspect of the present invention positioned, by way of example, in a trans-valvular configuration to provide right-heart assist. 
           [0056]      FIG. 20  corresponds to  FIG. 1  of U.S. Ser. No. 09/280,988, and is a schematic side view of a steerable cannula in the undeformed state in accordance with the first embodiment of U.S. Ser. No. 09/280,988; 
           [0057]      FIG. 21  corresponds to  FIG. 2  of U.S. Ser. No. 09/280,988, and is a schematic cross-sectional view of the steerable cannula of  FIG. 20  taken along line  2 - 2 ; 
           [0058]      FIG. 22  corresponds to  FIG. 3  of U.S. Ser. No. 09/280,988, and is a schematic side view of the steerable cannula in the deformed state in accordance with the first embodiment of U.S. Ser. No. 09/280,988; 
           [0059]      FIG. 23  corresponds to  FIG. 4  of U.S. Ser. No. 09/280,988, and is a schematic cross-sectional view of a steerable cannula having two cables in accordance with a second embodiment of U.S. Ser. No. 09/280,988; 
           [0060]      FIG. 24  corresponds to  FIG. 5  of U.S. Ser. No. 09/280,988, and is a schematic side view of a steerable cannula having a reinforcing wire in accordance with a third embodiment of U.S. Ser. No. 09/280,988; 
           [0061]      FIG. 25  corresponds to  FIG. 6  of U.S. Ser. No. 09/280,988, and is a schematic cut-away view of a steerable cannula in accordance with a fourth embodiment of U.S. Ser. No. 09/280,988; 
           [0062]      FIG. 26  corresponds to  FIG. 7  of U.S. Ser. No. 09/280,988, and is a schematic cross-sectional view taken along line  7 - 7  of  FIG. 25 ; 
           [0063]      FIG. 27  corresponds to  FIG. 8  of U.S. Ser. No. 09/280,988, and is a schematic side view of a steerable cannula having a preformed curve and an inflatable balloon formed at a distal end thereof in accordance with a fifth embodiment of U.S. Ser. No. 09/280,988; 
           [0064]      FIG. 28  corresponds to  FIG. 9  of U.S. Ser. No. 09/280,988, and is a schematic side view of the inflatable balloon of a fifth embodiment of U.S. Ser. No. 09/280,988, wherein the balloon is shown in the inflated state; 
           [0065]      FIG. 29  corresponds to  FIG. 10  of U.S. Ser. No. 09/280,988, and is a schematic cross-sectional view taken along line  10 - 10  of  FIG. 28 ; 
           [0066]      FIG. 30  corresponds to  FIG. 11  of U.S. Ser. No. 09/280,988, and is a schematic view showing a steerable cannula having a pigtail distal tip configuration in accordance with a sixth embodiment of U.S. Ser. No. 09/280,988; 
           [0067]      FIG. 31  corresponds to  FIG. 12  of U.S. Ser. No. 09/280,988, and is a schematic view showing a steerable cannula having a guidewire distal tip configuration in accordance with a seventh embodiment of U.S. Ser. No. 09/280,988; 
           [0068]      FIG. 32  corresponds to  FIG. 13  of U.S. Ser. No. 09/280,988, and is a schematic view showing a steerable cannula having a guidewire distal tip configuration in accordance with an eighth embodiment of U.S. Ser. No. 09/280,988; 
           [0069]      FIG. 33  corresponds to  FIG. 14  of U.S. Ser. No. 09/280,988, and is a schematic side view showing a steerable cannula used in a co-axial configuration in accordance with a ninth embodiment of U.S. Ser. No. 09/280,988, wherein the steerable cannula is advanced to a first relative position; 
           [0070]      FIG. 34  corresponds to  FIG. 15  of U.S. Ser. No. 09/280,988, and is a schematic side view showing a steerable cannula of  FIG. 33 , wherein the steerable cannula is advanced to a second relative position; and 
           [0071]      FIG. 35  corresponds to  FIG. 16  of U.S. Ser. No. 09/280,988, and is a schematic side view of a configuration in accordance with a tenth embodiment of U.S. Ser. No. 09/280,988. 
           [0072]      FIG. 36  corresponds to  FIG. 1  of U.S. Ser. No. 09/280,970, and is a schematic side view of a first embodiment of U.S. Ser. No. 09/280,970; 
           [0073]      FIG. 37  corresponds to  FIG. 2  of U.S. Ser. No. 09/280,970, and is a schematic cross-sectional view taken along line  2 - 2  of  FIG. 36 ; 
           [0074]      FIG. 38  corresponds to  FIG. 3  of U.S. Ser. No. 09/280,970, and is a schematic cross-sectional view taken along line  3 - 3  of  FIG. 36 ; 
           [0075]      FIG. 3  corresponds to  FIG. 4  of U.S. Ser. No. 09/280,970, and is a schematic view of a cannula in accordance with an embodiment in a surgical application; 
           [0076]      FIG. 40  corresponds to  FIG. 5  of U.S. Ser. No. 09/280,970, and is a schematic partial cut-away side view of a second embodiment of U.S. Ser. No. 09/280,970; 
           [0077]      FIG. 41  corresponds to  FIG. 6  of U.S. Ser. No. 09/280,970, and is a schematic cross-sectional view taken along line  6 - 6  of  FIG. 40 ; 
           [0078]      FIG. 42  corresponds to  FIG. 7  of U.S. Ser. No. 09/280,970, and is a schematic side view of a third embodiment of U.S. Ser. No. 09/280,970; 
           [0079]      FIG. 43  corresponds to  FIG. 8  of U.S. Ser. No. 09/280,970, and is a schematic side view of a fourth embodiment of U.S. Ser. No. 09/280,970; 
           [0080]      FIG. 44  corresponds to  FIG. 9  of U.S. Ser. No. 09/280,970, and is a schematic side view of a fifth embodiment of U.S. Ser. No. 09/280,970; 
           [0081]      FIG. 45  corresponds to  FIG. 10  of U.S. Ser. No. 09/280,970, and is a schematic side view of a sixth embodiment of U.S. Ser. No. 09/280,970; 
           [0082]      FIG. 46  corresponds to  FIG. 11  of U.S. Ser. No. 09/280,970, and is a schematic cross sectional view taken along line  11 - 11  of  FIG. 45 ; 
           [0083]      FIG. 47  corresponds to  FIG. 12  of U.S. Ser. No. 09/280,970, and is a schematic side view of a seventh embodiment of U.S. Ser. No. 09/280,970; 
           [0084]      FIGS. 48 and 49  correspond to  FIGS. 13 and 14 , respectively, of U.S. Ser. No. 09/280,970, and are schematic side views of an eighth embodiment of U.S. Ser. No. 09/280,970; 
           [0085]      FIG. 50  corresponds to  FIG. 15  of U.S. Ser. No. 09/280,970, and is a schematic cross-sectional view taken along line  15 - 15  of  FIG. 49 ; 
           [0086]      FIG. 51  corresponds to  FIG. 16  of U.S. Ser. No. 09/280,970, and is a schematic side view of a ninth embodiment of U.S. Ser. No. 09/280,970; 
           [0087]      FIG. 52  corresponds to  FIG. 17  of U.S. Ser. No. 09/280,970, and is a schematic side view of a tenth embodiment of U.S. Ser. No. 09/280,970; 
           [0088]      FIG. 53  corresponds to  FIG. 18  of U.S. Ser. No. 09/280,970, and is a schematic cross-sectional view taken along line  18 - 18  of  FIG. 52 ; and 
           [0089]      FIG. 54  corresponds to  FIG. 19  of U.S. Ser. No. 09/280,970, and is a schematic side view of an eleventh embodiment of U.S. Ser. No. 09/280,970. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0090]    Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation may be described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
         [0091]    The present invention involves an intravascular pump system for use in a number of broad ranging applications involving the augmentation of blood flow within the circulatory system of a patient. As will be described below, the intravascular blood pump system of the present invention overcomes the drawbacks of the prior art by providing a guide mechanism as part of the intravascular blood pump. This advantageously allows the intravascular blood pump to be selectively guided to a predetermined location within the circulatory system of a patient without the need for bulky supplemental guide mechanisms, such as a separate guide catheter. 
         [0092]    The intravascular pump assembly of the present invention is particularly suited for trans-valvular use, such as for left and/or right ventricular assist procedures. By way of example only, such ventricular assist procedures may be employed in cardiac operations including, but not limited to, coronary bypass graft (CABG), cardio-pulmonary bypass (CPB), open chest and closed chest (minimally invasive) surgery, bridge-to-transplant and/or failure-to-wean-from-bypass situations. It is to be readily understood, however, that the intravascular blood pump assembly and methods of the present invention are not to be limited to such applications. Moreover, while illustrated and described largely with reference to left-heart assist applications, it is to be readily understood that the principles of the present invention apply equally with regard to right-heart assist application, which are contemplated as within the scope of the present invention. These and other variations and additional features will be described throughout. 
         [0093]    Referring to  FIG. 1 , shown is a guidable intra-vascular blood pump system  10  according to a first broad aspect of the present invention shown, by way of example only, in a left-heart assist configuration within a human heart. The system  10  includes an intravascular blood pump  12 , a cannula  14 , and an “over-the-wire” type guide mechanism  16 . A drive cable assembly  18  and a motor assembly  20  are provided to drive the intravascular blood pump  12 . The “over-the-wire” guide mechanism  16  comprises a suitable guide element dimensioned to pass slideably through a central lumen extending through the drive cable  18 , blood pump  12 , and cannula  14 . Suitable guide elements may include any number of conventional guiding devices, including but limited to those employed in cardiology. By way of example only, the guide element is shown as a guide wire  22 . According to the present invention, the “over-the-wire” guide mechanism  16  provides the ability to selectively guide the blood pump  12  and cannula  14  to a predetermined position in the circulatory system of a patient, such as the trans-valvular position shown. 
         [0094]    To accomplish this, the guide wire  22  is first introduced into the vascular system of a patient through any suitable access point, such as through the use of the well known Seldinger technique. The guide wire  22  can then be advanced within the patient to a desired location within the circulatory system of the patient. This may be done using the control features of the guide wire  22  itself, or may be facilitated through the use of any number of supplemental guidance mechanisms or techniques to ensure the proper and efficient placement of the guide wire  22 . Such supplemental guidance techniques may include, but are not necessarily limited to, guide catheters and/or techniques involving ultra-sound or flouroscopy. Once the guide wire  22  is positioned at the desired location (such as in left ventricle as shown), the blood pump  12  and cannula  14  may thereafter be advanced along the guide wire  22  and positioned in the trans-valvular configuration shown. Under the operation of the motor assembly  20 , the blood pump  12  may be used for left-heart assist by selectively withdrawing blood from the left ventricle (through the interior of the cannula  14 ) for delivery outward through outflow apertures formed in the blood pump  12 . This outflow from the blood pump  12  flows along the exterior of the drive cable assembly  18  in a substantially axial fashion for arterial distribution throughout the body. 
         [0095]    Referring to  FIGS. 2-5 , an exemplary embodiment of the intravascular blood pump system  10  of  FIG. 1  will now be described. As shown in  FIG. 2 , the intravascular blood pump system  10  includes a coupler  24  and, as will be described in greater detail below, a purge fluid delivery system  26  for providing a two-way fluid flow within the drive cable assembly  18  during pump operation. The purge fluid delivery system  26  includes a fluid inlet conduit  28  for introducing pressurized purge fluid from a fluid source (not shown) for delivery into the blood pump  12 , and a fluid outlet conduit  30  to withdraw a return flow of purge fluid from the blood pump  12 . The motor coupler  24  establishes a mechanical connection between a motor (not shown) and a drive cable (not shown) for providing motive force to the blood pump  12  for pump operation. The drive cable assembly  18  includes a drive cable sheath  32  which, in addition to serving a purge fluid delivery function, also serves as a protective housing for the drive cable (not shown). Although shown in broken form for clarity, it will be appreciated that the drive cable assembly  18  (and all components thereof) may be provided in any suitable length sufficient for intravascular applications. That is to say, the length of the drive cable assembly  18  must be enough to reach between the motor coupler  24  and purge fluid delivery system  26 , located outside the patient, and the desired location within the patient&#39;s circulatory system where the blood pump  12  is to be positioned. 
         [0096]    The intravascular blood pump  12  is shown (by way of example only) as an axial flow intravascular blood pump. The blood pump  12  includes pump body  34 , a rotor shroud  36  having flow ports  38 , and an internally disposed rotor (not shown) having a shaft rotatably disposed within the pump body  34  and an impeller rotatably disposed within the rotor shroud  36 . The cannula  14  is fixedly attached to the rotor shroud  36  and may extend any suitable length therefrom depending upon the particular intravascular application. The cannula  14  preferably includes a plurality of ports or fenestrations  40  about its distal region, as well as an end port  42 , which allow for the ingress or egress of blood into or from the cannula  14  depending upon the operation of the blood pump  12 . That is to say, if the pump  12  is configured for left-heart assist as shown in  FIG. 1 , then the ports  40 ,  42  will allow the ingress of blood into the cannula  14  from the left ventricle. If, on the other hand, the blood pump  12  is configured for right-heart assist (i.e. with the pump  12  in the right atrium and the distal end of the cannula  14  located within the pulmonary artery), then the ports  40 ,  42  will allow the egress of blood from the cannula  14  into the pulmonary artery. (Details on right-heart assist applications will be discussed in greater detail below.) The pump  12  and cannula  14  may be dimensioned to any suitable diameter for intravascular applications. For example, the range of sizes may include, but is not necessarily limited to, 9 French to 30 French, although the range is more preferably from 14 French to 24 French, and most preferably from 18 French to 20 French. 
         [0097]    The “over-the-wire” type guide mechanism  16  includes the guide wire  22  and, as will be explained in greater detail below, a central lumen extending through the cannula  14 , blood pump  12 , drive cable assembly  18 , purge fluid delivery system  26 , and motor coupler  24 . As noted above, the central lumen is dimensioned to slideably receive the guide wire  22  such that the blood pump  12  and cannula  14  may be slideably advanced along the guide wire  22  to a desired location within the circulatory system of a patient after the guide wire  22  has been so positioned using conventional guidance techniques. It is to be readily understood that, while shown as a conventional guide wire  22 , the guide element forming part of the guide mechanism  16  of the present invention may include any number of well known guidance mechanisms depending upon the application, including but not limited to balloon catheters, imaging wires, and guide catheters dimensioned to be slideably received through the central lumen. For example, although not appropriate for retrograde progression (such as the left-heart application shown in  FIG. 1 ), a balloon catheter may be a suitable guidance mechanism for a right-heart assist application. In such a case, the balloon may be inflated and used as a “sail” to direct the catheter to a desired location (such as the pulmonary artery), after which point the blood pump  12  and cannula  14  can be advanced over the catheter to a trans-valvular configuration with the blood pump  12  in the right atrium and the ports  38 ,  40  of the cannula  14  in the pulmonary artery. 
         [0098]      FIGS. 3 and 4  further detail the construction of the blood pump  12 , cannula  14 , drive cable assembly  18 , and “over-the-wire” guide mechanism  16 . The blood pump  12  includes a rotor  44  having a shaft  46  and an impeller  48 . The shaft  46  is rotatably disposed within the pump body  34  via a bearing pack comprising, by way of example, ball bearing assemblies  50 ,  52  and spring  54 . Ball bearings assemblies  50 ,  52  are well known in the art, each comprising an inner race which rotates along with the rotor shaft  46 , an outer race which remains in a static and fixed position against the inner surface of the pump body  34 , and a plurality of ball bearings disposed between the inner and outer races. The spring  54  biases each bearing assembly  50 ,  52  axially away from one another to reduce axial play during pump operation. The shaft  46  is generally hollow and dimensioned to receive a cable adapter  60  therein for the purpose of coupling the rotor  44  to a drive cable  62  forming part of the drive cable assembly  18 . The drive cable  62  may be secured to the cable adapter  60  in any number of suitable fashions, including but not limited to the use of adhesives, crimping, and laser welding. These same techniques may be used to secure the cable adapter  60  within the shaft  46  of the rotor  44 . A radial seal  64  is provided in between the wall of the pump body  34  and a distal stepped region  66  on the rotor shaft  46 , the function of which will be described below. 
         [0099]    The impeller  48  includes a hub  56  and a plurality of blades  58  extending therefrom. The hub  56  is generally conical and, according to the first broad aspect of the present invention, is hollow throughout to form part of the central lumen of the guide mechanism  16 . In this regard, the hub  56  is preferably provided with a gasket or seal member  68  at its distal tip. The seal member  68  may be made of any suitable sealing material (including but not limited to silicone) such that the pump  12  and cannula  14  may be easily progressed along the guide wire  22  for delivery to a desired circulatory site. The seal member  68  should also be robust enough to prevent the ingress of blood into the interior of the rotor hub  56  during pump operation, whether the guide wire  22  remains in place or is fully withdrawn. The blades  58  are dimensioned to reside in close tolerance with the interior surface of the shroud  36 . In operation, the blades  58  impart both an axial and radial vector on the blood which causes it to flow outward through the flow ports  38  formed in the shroud  36 . As used herein, the term “axial flow” is deemed to include flow characteristics like that shown in  FIG. 3 , which include both an axial and slight radial component. It is to be readily appreciated that, although shown as an axial flow type, blood pump  12  may comprise any number of suitable types of intravascular blood pumps, including but not limited to so-called “mixed flow” intravascular blood pumps without departing from the scope of the present invention. 
         [0100]    The cannula  14  is coupled at its proximal end to the rotor shroud  36 . This may be accomplished in any number of fashions, including but not limited to the use of adhesives. This may also be facilitated by dimensioning the shroud  36  to include a narrow inlet region  70  capable of being received flushly within the proximal end of the cannula  14 . The inlet region  70  of the shroud  36  should preferably have a tapered interior surface for establishing a smooth flow transition between the cannula  14  and the region containing the impeller blades  58 . Although shown as a single integral element, it is to be understood that the pump body  34  and shroud  36  may comprise two separate (and sometimes separable) components, the significance of which will become apparent below. The pump body  34  and shroud  36  may be constructed from any number of suitable materials, including but not limited to stainless steel or other medical grade compositions or alloys. The cannula  14  may also be constructed from any number of suitable materials, including but not limited to medical grade plastics. As shown, the cannula  14  may also be fortified with spiral-wound reinforcement wire  72  within the walls of the cannula  14 . 
         [0101]    The drive cable assembly  18  includes the drive cable  62  and the drive cable sheath  32 . The drive cable  62  is coupled to the rotor  44  via the cable adapter  60 . The drive cable sheath  32  includes a central lumen  74  and a plurality of side lumens  76 . The central lumen  74  serves as a protective covering for the drive cable  62 . The central lumen  74 , along with the side lumens  76 , also forms part of the purge fluid delivery system  26  shown above in  FIG. 2 , which will be described in greater detail below. The side lumens  76  are provided in fluid communication with the fluid inlet conduit  28 , while the central lumen  74  is provided in fluid communication with the fluid outlet conduit  30 . The side lumens  76  are thus configured to deliver purge, fluid into the pump  12 , while the central lumen  74  is configured to transport purge fluid away from the pump  12  along the length of the drive cable  62 . 
         [0102]    The pressurized purge fluid within the side lumens  76  may take one of two flow paths upon entry into the pump  12 . One flow path passes through the interior of the pump  12  and onward past the radial seal  64  to prevent the ingress of blood into the pump body  34  during pump operation. More specifically, the purge fluid flows distally around the cable adapter  60 , through the ball bearing assemblies  50 ,  52 , and onward past the radial seal  64 . This egress of purge fluid past the radial seal  64  can be controlled to effectively thwart the ingress of blood past the radial seal  64 , which might otherwise cause clotting and/or pump damage. The other flow path is directed back out the central lumen  74  for delivery to the fluid outlet conduit  30 . In so doing, this flow path bathes the components of the pump  12  and/or drive cable  62  and thereby reduces frictional heating within the pump  12  and/or the central lumen  74  of the sheath  32  during pump operation. 
         [0103]    The “over-the-wire” guide mechanism  16  includes a central lumen through which the guide wire  22  may extend for the purpose of slideably advancing the blood pump  12  and cannula  14  into a desired position within the circulatory system of a patient. In the embodiment shown, this central lumen is established by forming and co-aligning the individual central lumens within each of the drive cable  62 , the cable adapter  60 , the shaft  46  and hub  56  of the rotor  44 , and the cannula  14 . In this regard, the drive cable  62  is preferably of wound-wire construction having a central lumen formed therein. The central lumens within the cable adapter  60 , rotor  44 , and gasket  68  may be formed via machining or molding processes. These central lumens should preferably be sized such that they permit the slideable passage of the pump  12  and cannula  14  therealong, but do not interfere with or constrain the guide wire  22  to cause inadvertent rotation of the guide wire  22  during pump operation. As noted above, it is also contemplated to remove the guide wire  22  after the pump  12  and cannula  14  are properly positioned in the patient. In this case, the gasket or seal  68  on the hub  56  should be robust enough to reseal after the guide wire  22  is withdrawn and prevent the ingress of blood into the interior of the rotor  44 . 
         [0104]    Referring to  FIG. 5 , the motor coupler  24  includes a housing  78 , a drive shaft adapter  80 , and a bearing assembly  82 . The drive shaft adapter  80  includes a drive shaft coupler  84  dimensioned to receive a drive shaft of a motor (not shown), and a drive cable coupler  86  dimensioned to receive the drive cable  62 . Any of a variety of attachment techniques may be employed to securely fasten the drive cable  62  to the drive cable coupler  86 , including but not limited to adhesives, crimping, and laser welding. The drive shaft adapter  80  is rotatably disposed within the housing  78  by the bearing assembly  82 . The bearing assembly  82  includes a sleeve  88  (which may alternatively be formed as an integral part of the housing  78 ) for retaining a pair of ball bearing assemblies  90 ,  92  and a spring  94  of the type described above. That is, each bearing assembly  90 ,  92  generally comprises an inner race which rotates along with the drive shaft adapter  80 , an outer race which remains in a static and fixed position against the inner surface of the retaining sleeve  88 , and a plurality of ball bearings disposed between the inner and outer races. The spring  94  is provided to bias each bearing assembly  90 ,  92  axially away from one another to reduce axial play during operation. 
         [0105]    The purge fluid delivery system  26  includes a housing  96  having a central lumen  98 , an inflow port  100 , and an outflow port  102 . The housing  96  is also dimensioned to matingly receive a portion of the motor coupler  24 . In this regard, a seal element  104  is provided sandwiched in between the housing  96  and housing  78  and including an aperture which extends about the drive shaft adapter  80  as it exits the housing  78  to prevent the ingress of purge fluid into the motor coupler  24 . A fluid guide structure  106  is also provided within the central lumen  98  for the purpose of separating the inflow and outflow ports  100 ,  102 . The fluid guide structure  106  includes a central lumen  108  through which the drive cable  62  extends, and an elevated portion  110  that retains an O-ring  112  against the inner surface of the central lumen  98  of the housing  96 . The drive cable sheath  32  is secured to the housing  96  such that the inflow port  100  is communicatively coupled to the side lumens  76 , and the outflow port  102  is communicatively coupled to the central lumen  74 . In this fashion, pressurized purge fluid may be introduced through the inflow port  100  via inflow conduit  28 , and removed through the outflow port  102  via outflow conduit  30 . By way of example, the inflow conduit  28  and outflow conduit  30  may be coupled to their respective ports  100 ,  102  via barbed connectors  114 . Similarly, the inflow and outflow conduits  28 ,  30  may be equipped with any number of suitable connectors (such as those illustrated by way of example in  FIG. 2 ) for establishing fluid communication with a source of pressurized fluid (not shown). The pressurized fluid source (not shown) may include, but is not necessarily limited to, the use of a syringe, an indeflator, a fluid delivery pump, or an accumulator arrangement to provide the requisite delivery of pressurized fluid. The purge fluid delivery system  26  thus provides a two-way transmission of purge fluid within the drive cable sheath  32  for the purposes of cooling the blood pump  12  and preventing the ingress of blood past the radial seal  64  and into blood pump  12 . 
         [0106]    Referring to  FIG. 6 , shown is a guidable intra-vascular blood pump system  120  according to a second broad aspect of the present invention. As will be described hereinafter, the intravascular blood pump system  120  differs from the intravascular blood pump system  10  described above only as to the type of guide mechanism employed. In the interest of clarity and consistency, then, like reference numerals will be used to denote like elements and distinctions pointed out where necessary. Moreover, due to the commonality of principles employed in both intravascular blood pump systems  10 ,  120 , a discussion to the level of detail set forth above is not deemed necessary with regard to the intravascular blood pump system  120 . Instead, those aspects in common with the intravascular blood pump  10  are hereby incorporated into the discussion of the intravascular blood pump system  120 . 
         [0107]    In its most general form, the intravascular blood pump system  120  of this second broad aspect of the present invention comprises the blood pump  12  and cannula  14  arrangement, wherein the cannula  14  is equipped with a “side-rigger” or “rapid exchange” guide mechanism  122 . In an important aspect of the present invention, the “rapid exchange” or “side-rigger” guide mechanism  122  includes a guide carriage  124  formed along at least a portion of the cannula  14 , and a suitable guide element (such as guide wire  22 ) dimensioned to pass slidably through a lumen (not shown) extending through the guide carriage  124 . The “rapid exchange” guide mechanism  122  thereby provides the ability to selectively guide the blood pump  12  and cannula  14  to a predetermined position in the circulatory system of a patient in the manner described above. Namely, the guide wire  22  may be first introduced into the vascular system of a patient through any suitable access point and guided to a desired location within the circulatory system of the patient, i.e. the left ventricle as shown. The blood pump  12  and cannula  14  may thereafter be advanced along the guide wire  22  and positioned in the trans-valvular configuration shown for providing left-heart assist. 
         [0108]      FIGS. 7-9  further illustrate the “side-rigger” or “rapid-exchange” guide mechanism  122  of this second broad aspect of the present invention. In a preferred embodiment, the “side-rigger” guide mechanism  122  includes a lumen  126  formed within the guide carriage  124 . The guide carriage  124  is preferably formed as an integral extension of the wall of the cannula  14 .  FIGS. 7 and 8  comport with the embodiment shown in  FIG. 6 , namely illustrating the guide carriage  124  formed along the exterior surface of the cannula  14 .  FIG. 9  illustrates an alternate embodiment wherein the guide carriage  124  may be formed along the interior surface of the cannula  14 . In either case, the guide wire  22  is advanced to a desired location in the vasculature of the patient, after which point the blood pump  12  and cannula  14  can be slidably advanced therealong for delivery to the desired location according to the present invention. The guide wire  22  may thereafter be withdrawn from the patient. If the guide carriage  124  is formed along the exterior surface of the cannula  14  (as shown in  FIGS. 7-8 ), then the cannula  14  should preferably be positioned so that the guide carriage  124  does not extend in a trans-valvular fashion. For example, with reference to  FIG. 6 , the guide carriage  124  should be positioned wholly within the left ventricle such that the pulsatile blood flow during beating heart procedures will not inadvertently pass through the side lumen  126  and pass through the aortic valve. 
         [0109]    The intravascular blood pump system  120  is constructed in virtually the same manner as the intravascular blood pump system  10  shown and described above, with the exception of the location of the respective guide mechanisms  16 ,  122 . More specifically, because the guide mechanism  122  is disposed along the side of the cannula  14 , there is no need to form a central lumen extending through the blood pump  12 , drive cable assembly  18 , purge fluid delivery system  26 , and motor coupler  24  as detailed above with regard to the intravascular blood pump system  10 . As such, these components need not be specially machined or molded to include such central lumens as was required with the intravascular blood pump system  10  set forth above. 
         [0110]    Referring to  FIG. 10 , shown is a guidable intravascular blood pump system  130  according to a third broad aspect of the present invention. Again, due to the commonality between many of the same components and features of the intravascular blood pump systems described above and the intravascular blood pump system  130 , like reference numerals will be used to denote like elements and distinctions pointed out where necessary. As will be explained in greater detail below, the intravascular blood pump system  130  employs yet another unique and useful guide mechanism according to the present invention. However, because many of the same components are employed, a discussion to the level of detail set forth above is not deemed necessary with regard to the intravascular blood pump system  130 . Instead, those aspects in common with the intravascular blood pumps described above are hereby incorporated into the discussion of the intravascular blood pump system  130 . 
         [0111]    In its most general form, the intravascular blood pump system  130  of this third broad aspect of the present invention comprises the blood pump  12  and cannula  14  arrangement, wherein a “guide catheter”  132  is provided as the guide mechanism for positioning the pump  12  and cannula  14  at a desired location within the circulatory system of the patient. More specifically, with brief reference to  FIG. 12 , the intravascular blood pump system  130  is formed in two separate assemblies according to the present invention: a conduit assembly  134  and pump assembly  136 . In its most basic form, the conduit assembly  134  comprises the guide catheter  132  and cannula  14  coupled to the rotor shroud  36 . The pump assembly  136  is constructed such that the pump body  34  and rotor  44  can be disengaged from the rotor shroud  36  and removed entirely from the conduit assembly  134 . Referring again to  FIG. 10 , this dual construction forms a significant feature of the present invention because it provides the ability to form the blood pump  12  at a desired location in a patient using two separate and distinct steps. The first step involves positioning the conduit assembly  134  (with the pump assembly  136  removed) within a patient such that the shroud  36  and cannula  14  are each disposed in a desired location, such as a trans-valvular configuration for cardiac assist procedures. In an important aspect, the task of positioning the conduit assembly  134  within the patient may be advantageously facilitated through the use of any number of well known guidance mechanisms, including but not limited to guide wires, balloon catheters, imaging wires, guide catheters, and/or techniques involving ultra-sound or flouroscopy. The second step in providing the intravascular blood pump system  130  of the present invention involves advancing the pump assembly  136  through the conduit assembly  134  such that the rotor  44  docks within the shroud  36  to form the pump  12  at the desired location. 
         [0112]    By way of clarification, the term “cannula” is used to denote cannula  14  because it serves a primary purpose of transporting fluid into the blood pump  12 , whereas the term “catheter” is used to denote the catheter  132  because it serves a primary purpose of guiding or directing devices or components (i.e. the pump assembly  136 ) to a desired location within the body. It is to be readily understood, however, that these terms are only used for convenience and in a general fashion such that the cannula  14  may serve certain guiding functions and the catheter  132  may serve certain fluid transportation functions without departing from the scope of the present invention. For example, the cannula  14  may be equipped with dedicated lumens to receive various guide mechanisms (such as guide wires, balloon catheters, selectively deformable elements such as Nitonol, etc). In similar fashion, the guide catheter  132  may be used to transport fluid to and/or from the patient, such as by providing apertures  138  along predetermined regions of the catheter  132 . 
         [0113]      FIG. 11  demonstrates a significant feature of the present invention involving the use of the guide catheter  132  to transport fluid to and/or from the patient. An optional perfusion assembly  140  is provided as part of the intravascular blood pump system  130  of the present invention. The perfusion assembly  140  includes a conduit  142  in fluid communication with the apertures  138 , which in this case are formed near the distal region of the guide catheter  132  a short distance downstream from the blood pump  12 . In use, blood will pass along the exterior of the guide catheter  132  for distribution throughout the body, as well as within the interior of the guide catheter  132  after passing into the apertures  138 . The perfusion assembly  140  may then be employed to selectively reroute blood from within the guide catheter  132  to a point within the patient&#39;s vasculature downstream from the point where the guide catheter  132  enters the body. A hemostasis valve assembly  146  of the perfusion assembly  140  permits the drive cable assembly  18  to pass through to the purge fluid delivery system  26  while preventing blood flow other than into the perfusion assembly  140 . A seal assembly  150  of the purge fluid delivery system  26  permits the drive cable  62  to pass through to the motor  20  while preventing the flow of purge fluid other than into and from the purge fluid delivery system  26 . The perfusion assembly  140  includes a control mechanism  148  for selectively controlling the distribution of perfusion blood flow from the perfusion assembly  140  into the patient. This control mechanism  148  may be automatic based on certain feedback criteria or manually operated. 
         [0114]      FIGS. 12-17  illustrate an exemplary construction of the intravascular blood pump system  130  according to the third broad aspect of the present invention. As shown in  FIG. 12 , the conduit assembly  134  may be selectively disengaged so as to remove the pump assembly  136  therefrom. According to the present invention, the conduit assembly  134  may be introduced (without the pump assembly  136 ) into the circulatory system of a patient and selectively guided such that the rotor shroud  36  and cannula  14  are positioned at a desired location. The pump assembly  136  can thereafter be selectively introduced into the conduit assembly  134 . A challenge in such a “back-loading” arrangement is ensuring that the pump assembly  136  docks appropriately within the rotor shroud  36  and is maintained in proper engagement during operation of the resulting pump  12 . 
         [0115]    An exemplary docking arrangement will now be described with reference to  FIG. 14 . In a preferred embodiment, the rotor  44  may be properly and accurately docked within the shroud  36  by forming angled mating surfaces on corresponding portions of the shroud  36  and pump body  34 . More specifically, an angled mating surface may be formed on the interior surface of the rotor shroud  36  along that portion extending proximally from the flow aperture  38 . A corresponding angled mating surface may be provided along the exterior surface of the pump body  34  along a distal portion thereof. The mating surfaces shown in  FIG. 14  may preferably be formed in the range from about 2 degrees to 10 degrees, and more preferably formed in the range from about 3 degrees to 6 degrees. Mating angles within these ranges are adequate to guide the distal end of the pump body  34  to a point generally flush with the proximal edge of the flow aperture  38  as shown in  FIG. 14 . In this fashion, the pump assembly  136  and the rotor shroud  36  combine to form the blood pump  12 . More importantly, this docking is carried out such that the rotor  44  and rotor blades  58  are maintained in proper position for efficient and safe pump operation. 
         [0116]    An exemplary biasing scheme for maintaining the pump assembly  136  in this docked relationship will now be described with reference to  FIGS. 12-13 and 16-17 . The conduit assembly  134  is preferably equipped with a male quick-connect coupling  152  capable of engaging with a female quick-connect coupling  154  forming part of the perfusion assembly  140  of the present invention. A bias spring  156  is provided in between the perfusion assembly  140  and the housing  96  of the purge fluid delivery system  26 . The bias spring  156  is preferably dimensioned so as to be in tension when the male quick-connect  152  is engaged within the female quick-connect  154  as part of the docking process of the present invention. As such, the bias spring  156  serves to maintain the pump assembly  136  in the docked position within the rotor shroud  36 . The bias spring  156  may be coupled to the housing  96  of the purge fluid delivery system  26  in any number of suitable fashions. One such coupling arrangement may comprise a female quick-connect coupling  158  attached to the housing  96  and a male quick-connect coupling  160  attached to the bias spring  156 . 
         [0117]    An exemplary embodiment of the perfusion assembly  140  is shown with reference to  FIGS. 12-13 and 17 . The perfusion assembly  140  shown includes the hemostasis valve  146  coupled to the female quick-connect coupling  154 . A length of tubing  162  extends between the opposing barb connectors of the hemostasis valve  146  and the female quick-connect coupling  154 . A continuous lumen is formed extending through the interior of the male quick-connect coupling  152 , the female-quick-connect coupling  154 , the tubing  162 , and the hemostasis valve  146 . The drive cable assembly  18  extends through this continuous lumen and exits through a Touehy-Borst hemostasis seal  164  which prevents the migration of blood out of the proximal end of the perfusion assembly  140 . A side-port  166  is disposed in fluid communication with the central lumen of the perfusion assembly  140 . In one embodiment, this side-port  166  may be equipped with a conduit  168  having a stop-cock  170  to selectively control the distribution of blood through a perfusion conduit (i.e. conduit  142  of  FIG. 11 ) coupled to the stop-cock  170 . It will be appreciated that this type of manual control system for selectively perfusing the patient may be replaced with control circuitry for automatically controlling the rate of perfusion. Such automatic perfusion may be based on control algorithms based on contemporaneous feedback or pre-programmed thresholds. 
         [0118]    The foregoing discussion details a host of inventive aspects forming part of the present invention. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concepts thereof. The following evidences, by way of example only, various additional aspects forming part of the present invention. 
         [0119]      FIG. 18  illustrates an alternate configuration of the intravascular blood pump system  130  of the third broad aspect of the present invention having an alternate bearing assembly, purge fluid delivery, and docking scheme. The bearing assembly includes a seal spring  182  and a bearing assembly  180 . The bearing assembly  180  includes an inner race  184 , an outer race  186 , and a plurality of balls  188  which enable the inner race  184  to rotate along with the rotor shaft  46  while the outer race  186  remains in a static and fixed position relative to an inner surface of the pump body  34 . An O-ring  190  is disposed within a groove formed in the rotor shaft  46  so as to maintain the bearing assembly  180  against the seal spring  182 . The O-ring  190  is further secured within the groove in the rotor shaft  46  via a contoured lip portion extending from the distal end of the cable adapter  60 . The proximal end of the cable adapter  60  flushly engages the drive cable  62 . 
         [0120]    The purge fluid delivery system of the embodiment shown in  FIG. 18  provides for a one way delivery of purge fluid to the blood pump  12 . That is, pressurized fluid (namely, fluid pressurized to some level elevated above the blood pressure in the surrounding vessel) is injected in between the drive cable  62  and the interior of the protective sheath  32  during operation. This serves to reduce any frictional heating that exists between the drive cable  62  and sheath  32 . The pressurized fluid also flows through the interior of the pump  12  such that, if the seal at  192  is broken, the pressurized fluid will flow past the open seal  192  and onward through the blood flow ports  38  formed in the shroud  36 . This serves to keep blood from entering the pump  12  in an effort to avoid clotting and/or damaging the pump  12 . 
         [0121]    The pump assembly  136  may be docked within the conduit assembly  134  in any number of different fashions without departing from the scope of the present invention. That is to say, the docking scheme shown in  FIG. 18  is set forth by way of example only and is not to be deemed limiting or restrictive as to numerous ways to temporarily engage or “dock” the pump assembly  136  within the conduit assembly  134 . The only requirement is that the pump assembly  136  and conduit assembly  134  dock such that the rotor  44  is disposed within the shroud  36  to provide the desired axial flow through the cannula  14  and out the shroud  36 . The exemplary docking scheme involves forming an annular engagement groove  194  along the interior of the shroud  36 , and forming a complementary annular ridge  196  along the exterior surface of the pump body  34 . During insertion, the pump assembly  136  will be advanced into the conduit assembly  134  until the annular ridge  196  on the pump body  34  engages within the groove  194  formed in the shroud  36 . This docking scheme is generally advantageous in that the engagement action between the annular ridge  196  and groove  194  will provide tactile feedback to the physician during the process of inserting the pump assembly  136  into the conduit assembly  134  such that the physician will be able to determine when the docking has been completed. 
         [0122]    As will be appreciated by those skilled in the art, the location of the annular ridge  196  and engagement groove  194  may be varied such that they are disposed closer or farther away from the flow apertures  38 . It may be advantageous to form these docking structures close to the flow apertures  38  in an effort to thwart the ingress of blood into the junction extending between the interior of the shroud  36  and the exterior surface of the pump body  34 . It is also contemplated to employ selectively inflatable structures, such as balloons, in an effort to temporarily engage or dock the pump assembly  136  within the conduit assembly  134 . In this regard, one or more lumens may be formed within the pump body  34  extending from the interior of the pump body  34  in fluid communication with a balloon disposed along the exterior surface of the pump body  34 . The pressurized fluid flowing within the interior of the pump body  34  may then be used to inflate the balloon, which will then engage within an annular groove in the shroud  36 , such as at  194 . Of course, the engagement structures may also be reversed without departing from the scope of the present invention. For example, the shroud  36  may be equipped with a fluid delivery lumen therein for inflating a balloon disposed on the interior surface of the shroud  36 , which may in turn be disposed within an annular engagement groove formed along the exterior surface of the pump body  34 . 
         [0123]    While this invention has been shown in use largely in during left-heart applications it is to be readily appreciated that this does not limit the applications of this invention for use in left heart support only. Rather, the guidable intravascular blood pump of the present invention can be utilized in right-heart support applications and a wide variety of other applications apparent to those skilled in the art. For example, with reference to  FIG. 19 , shown is an intravascular blood pump  200  (of the type shown and described above with reference to  FIGS. 2-5 ) configured for use in a right-heart support application. In this embodiment, the intravascular blood pump system  200  is equipped, by way of example, with an “over-the-wire” guide mechanism  16  comprising a balloon catheter  202 . It is to be readily appreciated that, although shown and described below in terms of an embodiment of the type shown in  FIGS. 2-5 , the intravascular blood pump systems  120 ,  130  disclosed herein may also be configured for use in right-heart applications. Such right-heart configurations, and others apparent to those skilled in the art based on the broad principles enumerated in this application, are contemplated as being within the scope of the present invention. 
         [0124]    The intravascular blood pump system  200  is shown positioned within the heart, such as may be advantageous to provide right heart support during beating heart surgery. To position the guidable intravascular blood pump system  200  in the right heart according to the present invention, a suitable guide element (such as balloon catheter  202 ) is first advanced to a desired location within the heart via the “sail” action of an inflated balloon. After the balloon catheter  202  is located in the desired position (such as in the pulmonary artery as shown), the intravascular blood pump system  200  according to the present invention may be advanced over the balloon catheter  202  and guided into a desired arrangement. For right heart support, this would involve advanced into the pump  12  and cannula  14  overt the balloon catheter  202  until the fluid inlet  204  is disposed within the vena cava (or right atrium) and the fluid outlet  206  is positioned within the pulmonary artery. The pump  12  may then be selectively (i.e. automatically or on-demand) controlled to transport blood from the vena cava (or right atrium) in a trans-valvular fashion through the tricuspid valve, the right ventricle, and the pulmonary valve for deposit within the pulmonary artery. Providing right-heart support during beating heart surgery advantageously overcomes conditions where cardiac output may become compromised during beating heart surgery, such as when the heart is lifted to gain access to posterior vessels, thereby avoiding the need for cardiopulmonary bypass. 
         [0125]    It is also contemplated as part of the present invention that the guidable intravascular blood pump systems can be introduced into the patient&#39;s vasculature to achieve the intravascular access into the right or left heart through any number of access points, including but not limited to the internal jugular vein, the brachiocephalic vein, carotid artery, axillary artery, femoral vein, femoral artery, and subclavian artery. The intravascular blood pump systems of the present invention may also be introduced via direct introduction, such as into the aorta, the atria, and the ventricles. As is well known in the art, such intravascular access may be achieved percutaneously through the use of the Seldinger technique or directly through the use of minimally invasive access techniques. 
         [0126]    Those skilled in the art will also appreciate that, although shown and described above in terms of “axial flow,” the present invention is not limited to the axial flow type intravascular blood pumps. Rather, the intravascular blood pumps  12  may comprise any number of suitable types of intravascular blood pumps, including but not limited to so-called “mixed flow” intravascular blood pumps, without departing from the scope of the present invention. 
         [0127]    With regard to the embodiments shown in  FIGS. 10-17 , it is furthermore contemplated that the guide catheter  132  may be separable from the conduit assembly  134  after the pump assembly  136  is docked within the shroud  36  to form the pump  12  at the desired location within the circulatory system of the patient. This may be accomplished by providing the guide catheter  132  in a detachable fashion via any number of suitable arrangements. By removing the guide catheter  132  after the pump  12  assembled, wound management of the access point into the patient&#39;s vasculature may be improved. This is due, in part, to the substantial reduction in size of the device extending into the patient (i.e. the drive cable assembly  18  as opposed to the larger diameter guide catheter  132 ). 
         [0128]    It is also contemplated to incorporate various pressure sensing and/or guidability features into at least one of the cannula,  14  and pump  12 . Such features may include, but are not necessarily limited to, those shown and described in commonly-owned and co-pending U.S. patent application Ser. No. 09/280,988 (filed Mar. 30, 1999) entitled “Steerable Cannula,” and U.S. patent application Ser. No. 09/280,970 (filed Mar. 30, 1999) entitled “Pressure Sensing Cannula,” the disclosures of which are hereby expressly incorporated by reference as if set forth herein in their entirety and physically incorporated as APPENDIX A and APPENDIX B respectively to the present specification. These pressure sensing features may include, but are not necessarily limited to, the use of fluid-filled lumens, piezo-electric pressure sensing elements, strain gauges, and analysis of the torque/current relationship (based on the dynamic pressure differential between the inlet and outlet of the pump). The guidability features may include, but are not necessarily limited to, the use of side lumens and deformable materials (i.e. Nitonol). 
         [0129]    Various pump and cannula arrangements have been described and shown above for providing right and/or left heart support wherein blood is deliberately re-routed through and past the right and/or left ventricle in an effort to reduce the volume of blood to be pumped by the particular ventricle. While “unloading” the ventricles in this fashion is preferred in certain instances, it is to be readily understood that the pump and cannula arrangements described herein may also be employed to “preload” the ventricles. Ventricular preloading may be accomplished by positioning the outflow cannula from the pump into a given ventricle such that the pump may be employed to fill or preload the ventricle with blood. This may be particularly useful with the right ventricle. On occasion, the right ventricle is not supplied with sufficient levels of blood from the right atrium such that, upon contraction, the right ventricle delivers an insufficient quantity of blood to the pulmonary artery. This may result when the right ventricle and/or right atrium are in a stressed or distorted condition during surgery. Preloading overcomes this problem by actively supplying blood into the right ventricle, thereby facilitating the delivery of blood into the pulmonary artery. The same technique can be used to preload the left ventricle and thus facilitate the delivery of blood from the left ventricle into the aorta.