Stylet for installing a retrograde coronary cannula

Abstract: A coronary cannula and installation stylet set, the stylet having a shaft (24) extending through the lumen of the coronary cannula to facilitate the installation of the cannula. The shaft (24) has a stiff but resilient proximal portion (30) and a deformable distal portion (32), shorter than the proximal portion (30), which can be deformed to hold the distal tip of the coronary cannula in a desired configuration to facilitate the insertion of the cannula into the coronary sinus.

Description: This invention relates to a coronary sinus cannula assembly for the retrograde infusion of cardioplegia solution into the coronary sinus of a patient's heart. Cardioplegia is a commonly used technique for protecting the heart during heart surgery in which a cooled cardioplegia solution, for example a potassium solution, is circulated through the heart. The cardioplegia solution stops the heart and reduces its temperature to minimize damage to the heart. Cardioplegia is often administered through the aorta in the antegrade direction, i.e., the direction of normal blood flow. However, there is increasing interest in administering cardioplegia in the retrograde direction, i.e., opposite the direction of normal blood flow. Retrograde administration of cardioplegia has been used in patients having critical coronary artery stenosis that would have made the antegrade administration of cardioplegia difficult and inefficient, and with patients suffering from aortal valve disease. Retrograde sinus catheters particularly adapted for the retrograde administration of cardioplegia are disclosed in EP-A-0 567 976. There are two principle techniques for installing a coronary cannula in the coronary sinus for the administration of cardioplegia. The first is known as the "open atrium" technique in which the right atrium of the heart is substantially opened with a large incision so that direct access is provided to the coronary sinus. A disadvantage of this technique is that it makes it more difficult to drain venous blood from the vena cava and to drain blood from the right atrium. An alternative is to use a "blind" procedure in which only a small incision is made to gain access to the right atrium and the coronary sinus. It can be very difficult to manipulate the coronary cannula, which is typically small and flexible, into the proper position in the coronary sinus through this small puncture. From US-A-4 846 186 a cannula assembly according to the preamble of claim 1 is known which discloses a flexible guidewire for inserting both diagnostic and therapeutic catheters. The guidewire includes an initial uniform diameter core segment coated with "TEFLON™" material. The initial core segment tapers to a second constant diameter portion that is surrounded by a flexible spring tip. The core tapers from the second constant diameter portion in a region where the flexible spring separates from the core. The core is flattened in that region to increase flexibility within the flexible spring. The guidewire is inserted along a tortuous path through the patient's cardiovascular system before a catheter is advanced along the guidewire. Generally, the method of installing a coronary cannula comprises providing a coronary cannula with a stylet extending through the lumen of the cannula. The stylet has a handle and a shaft that extends through the lumen with a stiff but flexible proximal portion, and a deformable distal portion. The shaft is sufficiently long that the deformable distal portion extends generally to the tip of the coronary cannula. The tip of the coronary cannula is then shaped by deforming the deformable distal portion of the stylet inside the lumen to facilitate its insertion through an incision in the right atrium and into the coronary sinus. The tip of the coronary cannula is then manipulated into the coronary sinus by steering the shaped tip by manipulating the handle. After the tip of the coronary cannula is in place, the cannula is anchored, for example by inflating a balloon at the tip of the cannula provided for that purpose, and the stylet can be drawn from the lumen of the coronary cannula. Generally, a coronary sinus cannula assembly of the invention is useful for the retrograde infusion of cardioplegia solution into the coronary sinus of a patient's heart. The cannula assembly comprises a cannula and a stylet. The cannula has at least an infusion lumen extending longitudinally through the catheter, and proximal and distal ends. The stylet comprises a handle defining a proximal end of the stylet, and a shaft extending from the handle. The shaft of the stylet is adapted to fit within the infusion lumen of the catheter. The shaft comprises a generally elongate malleable wire having proximal portion and distal portions and a generally circular cross section, and a generally elongate sleeve surrounding the proximal portion of the malleable wire. The sleeve and malleable wire are mounted to the handle so that neither the sleeve or malleable wire can be removed from the handle in normal use of the stylet. The sleeve is longer than the distal portion of the malleable wire and relatively stiff in comparison with the malleable wire to provide stiffness to a proximal portion of the cannula. The distal portion of the malleable wire extends distally from the sleeve, and is readily deformable in comparison with the sleeve, thereby facilitating deforming the malleable wire to hold the distal portion of the cannula in a desired configuration to facilitate the insertion of the cannula into the coronary sinus. The shaft is substantially completely received in the lumen of the cannula with the distal portion of the shaft heing surrounded by the cannula. The stylet and catheter are inserted into the coronary sinus as a unit, and the stylet is then removed from the cannula. The coronary cannula is preferably provided with the stylet already in the lumen, although they could be provided separately, and the stylet inserted into the lumen before the installation of the cannula. With the stylet inside the lumen of the coronary cannula, the tip of the coronary cannula can be configured to pass readily through an incision in the right atrium and into the coronary sinus. The malleable distal portion of the stylet holds the tip of the cannula in the desired preformed configuration, while the stiffer, flexible proximal portion of the stylet allows the cannula to flex and bend sufficiently as the tip of the cannula is manipulated into the coronary sinus. The method of installing the coronary cannula and the stylet apparatus for installing the cannula allow the cannula to be quickly inserted into the coronary sinus for the prompt administration of cardioplegia solution. The stylet apparatus also helps the surgeon gauge the depth of the tip to facilitate proper placement. The method and apparatus provide for the accurate placement of the cannula, and hold the cannula in place until it is anchored, for example by inflating a balloon on the cannula. These and other features and advantages will be in part apparent, and in part pointed out, hereinafter. Fig. 1 is a view of a stylet constructed according to the principles of this invention, inserted in the lumen of a coronary cannula, shown as it would be used to manipulate the cannula into the coronary sinus; Fig. 2 is a partial side elevation view of the stylet; Fig. 3 is an end elevation view of the stylet taken along the plane of line 3-3 in Fig. 2; Fig. 4 is an enlarged partial longitudinal cross-sectional view taken along the plane of line 4-4 in Fig. 2; Fig. 5 is a vertical cross-sectional view of the stylet taken along line 5-5 in Fig. 2; Fig. 6 is a vertical cross-sectional view of the stylet taken along the plane of line 6-6 in Fig. 4; and Fig. 7 is a partial side elevational view of another embodiment of the stylet of the invention. Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. A stylet apparatus for installing a coronary cannula in a coronary sinus is indicated generally at 20 in Figs. 1 and 2. The stylet 20 comprises a handle 22 and a shaft 24 extending from the handle and adapted to fit inside the lumen L of a coronary cannula C. (See Fig. 1). In practice, the coronary cannula C can be provided premounted on the shaft 24 of a stylet 20, to facilitate the proper installation of the cannula C in the coronary sinus. Alternatively the stylet 20 and the cannula C could be provided separately. The handle 22 of the stylet 20 may have a flat base 26, and a finger grip 28, so that the handle 22 can be grasped like a pistol, if desired. Of course some other style of handle could be provided, such as the handle 102 of the stylet 100 shown in Figure 7. The handle 22 is preferably made from a molded plastic, such as ABS, although the handle 22 could be made from any other suitable material. The shaft 24 of the stylet 20 preferably has a stiff but flexible proximal portion 30, and a shorter, malleable distal portion 32. As noted above, the shaft 24 is sized to fit in the lumen L of a coronary cannula C, and is sufficiently long that the distal end of the shaft 24 is closely adjacent to, but does not protrude from, the distal end of the coronary cannula C. (See Fig. 1). The distal portion 32 of the shaft 24 is sufficiently malleable that it can be shaped by hand to a configuration to facilitate the insertion of the cannula C and stylet 20 into the coronary sinus, yet the distal portion 32 is sufficiently stiff to substantially retain this shape as the tip of the cannula C and stylet 20 are manipulated into the coronary sinus. The proximal portion 30 of the shaft 24 is sufficiently stiff to allow the tip of the stylet 20 and cannula C to be steered by manipulating the handle 22. The proximal portion 30 is preferably not so rigid that it cannot be deformed by hand, for example to form a large radius arc in the proximal portion to facilitate installation of the cannula C. The relative lengths of the proximal and distal portions 30 and 32 are important to the steerability of the stylet 20 and cannula C. The distal portion 32 of the stylet 20 must be sufficiently long to hold the shape of the tip of the cannula mounted on the stylet 20. However, the distal portion 32 must be sufficiently short so that the cumulative effect of the flexibility of the distal portion 32 does not unduly interfere with the ability to steer the stylet 20 and cannula C. The distal portion 32 is preferably shorter than the proximal portion 30, and is preferably between 3.8 - 15.25 cm (1.5 and 6 inches) and most preferably between about 5.1 and 7.6 cm (2 and 3 inches) long. The proximal portion 30 is preferably between about 22.9 and 25.4 cm (9 and 10 inches) long so that the overall length of the shaft 24 is about 30.5 (12 inches). The shaft 24 preferably comprises a long, malleable wire 34 extending from the handle 22. The wire 34 is preferably made of a medical grade stainless steel, such as an SS 303 or SS 304 stainless steel, or other suitable material. The wire is dead soft (annealed), and of sufficient diameter that the wire can be easily shaped by hand into a desired configuration yet hold its shape while the cannula C and stylet 20 are manipulated into the coronary sinus. The wire preferably has a stiffness of between about 0.005 in/in and 0.025 in/in (most preferably 0.01-0.02 in/in (e.g., 0.015 in/in)) as determined by a standard Tenius-Olsen stiffness test with a 30 gram weight at a 0.75 inch deflection. See Federal Military Specification GGN-196 and ASTM D747, regarding Tenius-Olsen testing. The appropriate diameter may vary, depending on the size of the cannula C and the type of material used. For an SS 303 or 304 stainless steel a diameter of 0.1016 cm (0.040 inches) has been found to be satisfactory. The wire must be sufficiently stiff to retain its shape, but it must be sufficiently flexible to be comfortably manipulated by the surgeon by hand without damaging the cannula C. Also the wire must not be so stiff that it can puncture the tissue surrounding the coronary sinus. An advantage of the malleable wire is that for a given tip sharpness, the greater the flexibility, the greater force required to penetrate a given structure, for example the wall of the coronary sinus. Penetration pressure can be measured using an Instron Stress Machine to push a test piece through a standard medium, such as a 3 mm or 5 mm thick polyethylene sheet. The inventors conducted such tests measuring the puncture pressure at 7.6 cm (3 inches) from the tip when formed in a "C" and 15.2 cm (6 inches) from the tip and found that the average puncture pressure for ten repetitions is significantly higher with inventors' compound stylet 20. This means that greater force can be applied to the inventors' stylet 20 without puncturing the heart tissue. The proximal portion of the wire 34 ( i.e. , the portion adjacent the handle 22) is surrounded by a tubular sheath 36. The sheath 36 stiffens the proximal portion of the wire, forming the relatively stiff proximal portion 30 of the shaft 24. For a wire diameter of about 0.1016 cm (0.040 inches), the sheath 36 can be a 14 gauge stainless steel tube. Of course, with different wire diameters, different tube gauges can be used. The section of the wire 34 covered by the sheath 36 forms the stiff but flexible proximal portion 30. The compound construction with the wire 34 extending through the sheath 36 prevents the proximal portion 30 from kinking. The distal portion 32 of the wire 34 protruding from the sheath 36 forms the malleable distal portion 32 of the shaft. The compound construction of the shaft 24 is relatively simple and inexpensive to manufacture. The fact that the wire 34 extends the length of the shaft 24 reduces the risk that the distal portion 32 will break off or separate from the shaft 24. The wire 34 preferably has a coating 40, which may be a nylon, such as "ZYTEL 408™" nylon resin, or other suitable plastic. "ZYTEL 408™" is a trademark used in connection with a nylon resin available from E.I. Du Pont De Nemours & Company, Wilmington, Delaware. The coating 40 is preferably colored so that it is visible through the walls of the cannula C in which it is placed. The color of the coating 40 provides an indication of the depth of penetration of the tips of the cannula C and stylet 20 into the heart atrium, which helps to indicate when the tip of the cannula C is properly placed. At the point where the colored coating is no longer visible, the surgeon knows that the tips of the cannula C and stylet 20 are at a depth corresponding to the length of the proximal portion 30. This helps the surgeon to avoid inserting the cannula C past the coronary sinus, and possibly damaging the heart. The entire stylet 20 is preferably coated with a silicone-based lubricant to facilitate the removal of the stylet 20 after the cannula C is properly placed in the coronary sinus. The lubricant allows the stylet 20 to be withdrawn without pulling the coronary cannula C from the heart. The coating 40 also facilitates the removal of the deformed distal portion 32 from the cannula C with a minimum of disruption. OPERATION A coronary cannula C is preferably provided in a sterile package, already mounted on the shaft 24 of a stylet 20. The surgeon bends the tip of the cannula C, deforming the distal portion 32 of the shaft 24, to the desired configuration to facilitate the installation of the cannula C in the coronary sinus. The distal portion 32 deforms to hold the end of the coronary cannula C in the desired shape. An incision is made in the right atrium, and the coronary cannula C and stylet 20 are manipulated to bring the tip of the cannula C into the coronary sinus. The amount of colored coating 40 that is visible through the wall of the cannula C indicates to the surgeon the depth of the cannula tip in the heart. When the coronary cannula C is properly placed in the coronary sinus, it is anchored by means known in the art, for example, by inflating a balloon provided on the cannula C for that purpose. Once the coronary cannula C is firmly anchored, the stylet 20 is removed from the cannula C. The lubricant coating facilitates the removal of the stylet 20 from the coronary cannula C with a minimum of disruption to the cannula C. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims: A coronary sinus cannula assembly for the retrograde infusion of cardioplegia solution into the coronary sinus of a patient's heart, the cannula assembly comprising: a cannula (C) having at least an infusion lumen (L) extending longitudinally through the cannula, the cannula (C) having proximal and distal ends; and a stylet (20; 100) comprising a handle (22; 102) defining a proximal end of the stylet (20; 100), and a shaft (24) extending from the handle (22; 102) and having a proximal and a malleable distal portion and adapted to fit within the infusion lumen (L) of the cannula (C), the assembly being characterized in that the shaft (24) comprises: a generally elongate malleable wire (34) having a generally circular cross section; and a generally elongate sleeve (36) surrounding the proximal portion of the malleable wire (34), the sleeve (36) being longer than the distal portion (32) of the malleable wire (34) and relatively stiff in comparison with the malleable wire (34) to provide stiffness to a proximal portion of the cannula (C), the sleeve (36) and malleable wire (34) being mounted to the handle (22; 102) so that neither the sleeve (36) or malleable wire (34) can be removed from the handle (22; 102) in normal use of the stylet (20: 100); the distal portion (32) of the malleable wire (34) extending distally from the sleeve (36), the distal portion (32) of the malleable wire (34) being readily deformable in comparison with the sleeve (36), thereby facilitating deforming the malleable wire (34) to hold the distal portion of the cannula (C) in a desired configuration to facilitate the insertion of the cannula (C) into the coronary sinus; the shaft (24) being substantially completely received in the lumen (L) of the cannula (C) with the distal portion (32) of the shaft (24) being surrounded by the cannula (C), whereby the stylet (20; 100) and cannula (C) are inserted into the coronary sinus as a unit and the stylet then removed from the cannula. A coronary sinus cannula assembly according to claim 1 further characterized in that a plastic coating (40) is provided on the malleable wire (34). A coronary sinus cannula assembly according to claim 2 further characterized in that the plastic coating (40) is colored so that it is visible through the cannula (C), thereby providing an indication of the depth of insertion of the cannula (C) and stylet (20; 100). A coronary sinus cannula assembly according to any of claims 1-3 further characterized in that the malleable wire (34) is an annealed stainless steel. A coronary sinus cannula assembly according to any of claims 1-4 further characterized in that the malleable wire (34) has a Tenius-Olsen stiffness of between about 0.005 in/in and about 0.025 in/in. A coronary sinus cannula assembly according to any of claims 1-5 further characterized in that the deformable distal portion (32) of the malleable wire (34) has a length of between about 40mm and 150mm, and the sleeve (36) has a length of between 230mm and 250mm. A coronary sinus cannula assembly according to any of claims 1-6 wherein the cannula (C) further includes an inflatable balloon.

Inventors: BOYKIN CHRISTOPHER M, VAALBURG THOMAS T, BOYKIN, CHRISTOPHER M., VAALBURG, THOMAS T., BOYKIN, CHRISTOPHER M., C/O MINNESOTA MINING AND, VAALBURG, THOMAS T., C/O MINNESOTA MINING AND
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1993
Main classification: A61M25
IPC codes: A61M25, A61B17, A61M5, A61M31