US20110112353A1 - Bifurcated outflow cannulae - Google Patents

Abstract

A bifurcated cannula for directing blood into the arterial system. The bifurcated cannula including an ingress channel and first and second egress channels. The first egress channel directs a first portion of the blood entering the bifurcated cannula into the arterial system in a first direction. The second egress channel directs a second portion of the blood entering the bifurcated cannula into the arterial system in a direction that opposes the first direction.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application claims the priority of U.S. Provisional Patent Application Ser. No. 61/259,347, filed on Nov. 9, 2009 (pending), the disclosure of which is incorporated by reference herein.
TECHNICAL FIELD
• The present invention relates generally to devices for assisting the heart in moving blood through the body; more specifically the invention relates to pump outflow cannulae.
BACKGROUND
• The circulatory system of the human body transports blood containing chemicals, such as metabolites, hormones, and cellular waste products, to and from the cells. This organ system includes the heart, blood, and a vascular network. Veins are vessels that carry blood toward the heart while arteries carry blood away from the heart. The human heart consists of two atrial chambers and two ventricular chambers. Atrial chambers receive blood from the veins and the ventricular chambers, which include larger muscular walls, pump blood from the heart. Movement of the blood is as follows: blood enters the right atrium from either the superior or inferior vena cava and moves into the right ventricle. From the right ventricle, blood is pumped to the lungs via pulmonary arteries to become oxygenated. Once the blood has been oxygenated, the blood returns to the heart by entering the left atrium, via the pulmonary veins, and flows into the left ventricle. Finally, the blood is pumped from the left ventricle into the aorta and the vascular network.
• In some instances, it becomes necessary to maintain fluidic communication with the vascular network. For example, a circulatory assist system uses a pump to aid in moving blood through the vascular network, thereby relieving the symptoms associated with congestive heart failure (commonly referred to as heart disease). The pump of the circulatory assist system includes inflow and outflow cannulae. Often the inflow cannula connects the left side of the heart to the pump; the outflow cannula connects the pump to the arterial network.
• However, the fluidic output of the pump will often greatly exceed the natural fluid capacity of the particular artery used for implanting the outflow cannula. The insufficiency of the venous network to then immediately compensate for the increased blood inflow may result in edema of the extremity immediate to the implanted outflow cannula. While the venous network may adapt and compensate over time, it would be beneficial to have devices that better distribute the fluid flow from the pump in a manner that would prevent the initial occurrence of swelling.
SUMMARY
• In one illustrative embodiment, the present invention is directed to a bifurcated cannula for directing blood into the arterial system. The bifurcated cannula including an ingress channel and first and second egress channels. Blood from a pump flows into the bifurcated cannula through the ingress channel. The first egress channel directs a first portion of the blood entering the bifurcated cannula into the arterial system in a first direction. The second egress channel directs a second portion of the blood entering the bifurcated cannula into the arterial system in a direction that opposes the first direction.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a diagrammatic view of a circulatory assist system with the outflow of the pump being connected to the right subclavian artery by a bifurcated cannula, with the heart shown in cross-section.
• FIG. 2 is a perspective view of one exemplary embodiment of a bifurcated outflow cannula connected to the right subclavian artery and an implantable pump.
• FIG. 3 is a cross-sectional view of the bifurcated outflow cannula shown inFIG. 2.
• FIG. 4 is a perspective view of an exemplary method of removing the bifurcated outflow cannula and connecting the stent grafts.
• FIG. 5A is a cross-sectional view of another embodiment of a bifurcated outflow cannula with a channel fitting.
• FIG. 5B is a view similar toFIG. 5A, but showing the channel fitting assembled with the bifurcated outflow cannula.
• FIGS. 6-8 are cross-sectional views of additional embodiments of the bifurcated outflow cannulae.
• FIG. 9 is a diagrammatic view of an alternate method of implanting the circulatory assist system, with the heart shown in cross-section.
DETAILED DESCRIPTION
• FIG. 1 illustrates an implantedcirculatory assist system10. For illustrative purposes, certain anatomy is shown including theheart12 of apatient14 having aright atrium16, aleft atrium18, aright ventricle20, and aleft ventricle22. Blood from the left and rightsubclavian veins24,26 and the left and rightjugular veins28,30 enters theright atrium16 through thesuperior vena cava32 while blood from the lower parts of the body enters theright atrium16 through theinferior vena cava34. The blood is pumped from theright atrium16, to theright ventricle20, and to the lungs (not shown) to be oxygenated. Blood returning from the lungs enters theleft atrium18 viapulmonary veins36 and is then pumped into theleft ventricle22. Blood leaving theleft ventricle22 enters theaorta38 and flows into the leftsubclavian artery40, the leftcommon carotid42, and thebrachiocephalic trunk44 including the rightsubclavian artery46 and the rightcommon carotid48.
• With respect to the implantedcirculatory assist system10, aflexible cannula body50 extends from within theleft atrium18, through theintra-atrial septum52, and percutaneously to avascular access site54 in the rightsubclavian vein26. Theflexible cannula body50 is attached to aninput port56 of animplantable pump58. Though not shown, theflexible cannula body50 may alternatively be surgically implanted into theheart12 and extend to thepump58 through the thoracic cavity.
• Thepump58 may be an axially-driven pump with an impeller (not shown). Those skilled in this art, however, recognize that other types of pumps may be used in other embodiments but may include pumps such as those described in U.S. application Ser. No. 11/627,444, published as 2007/0197854, which is incorporated herein by reference in its entirety. Thesuitable pump58 for use with thecirculatory assist system10 may be capable of pumping blood.
• Acable60 can extend transdermally from thepump58 to a position in the abdomen where thecable60 exits thepatient14 and may connect to a power supply (not shown). Suitable power supplies may be any universal-type power supply that sends power to thepump58 via thecable60 and may include, but is not limited to, a rechargeable battery pack.
• The physician may position theimplantable pump58 at least subcutaneously and, optionally, submuscularly in apump pocket62 located near thevascular access site54, or alternatively, maintain thepump58 externally.
• A bifurcatedoutflow cannula64 connects anoutput port66 of theimplantable pump58 to a suitable artery, illustrate here as the rightsubclavian artery46. One skilled in the art would understand that while the bifurcatedoutflow cannula64 is illustrated as extending over the rightsubclavian vein26 to the right subclavian artery, in practice the bifurcatedoutflow cannula64 would likely reside beneath the rightsubclavian vein26.
• FIGS. 2 and 3 illustrate the bifurcatedoutflow cannula64 formed as a y-connector having aningress channel68 and first andsecond egress channels70,72. Thefirst egress channel70, as illustrated, directs blood into the rightsubclavian artery46 via afirst stent graft74 and in a direction that opposes (i.e., retrograde) the native blood flow direction of theright artery46, illustrated byarrow75. Thesecond egress channel72, as illustrated, directs blood into theartery46 via asecond stent graft76 and in a direction that is the same (i.e., radial) as the native blood flow direction of the rightsubclavian artery46. Thestent grafts74,76 may be any commercially-available self expanding, covered, endovascular stent graft, such as the FLAIR, which is manufactured by Bard Peripheral Vascular (Tempe, Ariz.) or the covered WALLSTENT by Boston Scientific (Natick, Mass.). As illustrated, the size of thestent grafts74,76 are selected to allow for a minimum of about 5 cm engagement within the vascular structure and up to about 10 cm of length outside of the vascular structure for connection to the bifurcatedoutflow cannula64; however, the size and lengths of thestent grafts74,76 should not be limited to those specifically shown.
• FIG. 3 illustrates the further details of the bifurcatedoutflow cannula64 in cross-section. Thebifurcated outflow cannula64 may be machined from a metallic material, for example titanium, and polished to minimize the incidence of thrombus formation; alternatively, thebifurcated outflow cannula64 may be molded from a polymeric material, such as silicone or urethane.
• Theegress channels70,72 are constructed to permit a desired, relative amount of blood flow in the radial and retrograde directions. As shown, thesecond egress channel72 branches distal to thefirst egress channel70; however, other arrangements may be used. Theegress channels70,72 are constructed withlumens78,80 having relative cross-sectional areas that are selected to provide a retrograde:radial flow ratio that is approximately 80:20 to meter the blood flow from thepump58. Accordingly, a first flow through thefirst egress channel70 in the retrograde direction will be high volume while a second flow through thesecond egress channel72 in the radial direction will be low volume. Though not specifically shown, it is possible to construct the cross-sectional areas such that the ratios are 50:50 or other ratios as desired, but generally the volume directed in the retrograde direction will meet or exceed the volume directed in the radial direction.
• Referring now toFIGS. 1,2, and3, in use, the physician creates first and secondvascular incisions82,84 in the appropriate vascular structure, illustrated here as the rightsubclavian artery46. The first andsecond stent grafts74,76 are directed into and deployed in the rightsubclavian artery46 in a manner that is well known to one that is skilled in the art and that accommodates placement of thebifurcated outflow cannula64.
• The physician then positions the proximal ends of thestent grafts74,76 over an outer surface of therespective egress channels70,72 of thebifurcated outflow cannula64. The outer surface may be constructed to include one ormore barbs86,88 for providing resistance against the undesired removal of thestent grafts74,76.Graft collets90,92 may then be used to clamp and secure thestent grafts74,76 onto theegress channels70,72 in a manner that is known.
• If desired, the physician may connect anextension tube94 between theingress channel68 and theoutflow port66 of thepump58. In this way, thepump58 may be positioned at a desired distance from the rightsubclavian artery46. Theextension tube94 may be constructed from a biodurable, low durometer thermoplastic or thermoset elastomer material. Coupling of theextension tube94 to theingress channel68 may include directing a distal end of theextension tube94 over the outer surface of theingress channel68, which may also include one ormore barbs96. Theextension tube94 may then be secured with acollet98 and in a manner that is similar to the methods described above. Anothercollet100 may be used to secure theextension tube94 to theoutflow port66 of thepump58.
• With the fluidic coupling complete, thecirculatory assist system10 may be used to aid theheart12 in pumping the patient's blood through the vascular network as was shown inFIG. 1. Accordingly, blood flow can proceed in the native manner with oxygenated blood traveling from theleft atrium18 into theleft ventricle22 to theaorta38. From theaorta38, blood moves into the leftsubclavian artery40, the leftcommon carotid42, and thebrachiocephalic trunk44. Blood flow may also proceed along the artificial path by entering theflexible cannula body50 from theleft atrium18 and traveling through the lumen of theflexible cannula body50 to thepump58.
• From thepump58, blood flows into thebifurcated outflow cannula64, which is then distributed in a manner that is consistent with the selected retrograde:radial ratio. For example, with the illustratedbifurcated outflow cannula64 having the retrograde:radial ratio of 80:20, the majority of the blood will be directed in the retrograde direction. Because thepump58 is typically operated within a range of about 2 L/min to about 3 L/min and the native flow rate of the rightsubclavian artery46 is about 0.5 L/min, the blood pumped in the retrograde direction will overpower the native flow into the rightsubclavian artery46. Accordingly, the net blood flow in the rightsubclavian artery46 that is distal to thefirst egress channel70 will be in the retrograde direction into thebrachiocephalic trunk44, and even theaorta38. From there, the blood is redistributed, for example, into other arteries, such as thecarotid arteries42,48 and thevertebral artery104. The other 20% of the blood flow is directed radially, in the native blood flow direction of the rightsubclavian artery46 and, accordingly, will enter theaxillary artery106 and thebrachial artery108 of theright arm112. In this way, blood is supplied to the patient'sright arm112 or the extremity downstream of the select artery while not overwhelming the venous capacity to remove the same and thus eliminating edema.
• In some patients, there may be a time after the surgery in which thecirculatory assist system10 is no longer necessary. Thus, it would be beneficial to remove the unnecessary components, such as theimplantable pump58 and theflexible cannula body50. However, the decrease in blood flow in the portion of the rightsubclavian artery46 between thestent grafts74,76 will have caused the vessel to thrombus completely and become occluded within a short time after thecirculatory assist system10 is implanted. One exemplary method of reversing the procedure and continuing blood flow through the rightsubclavian artery46 is illustrated inFIG. 4.
• As shown, once the pump58 (FIG. 1) and flexible cannula body50 (FIG. 1) have been removed, the extension tube94 (FIG. 2) and bifurcated outflow cannula64 (FIG. 2) are also removed. Thestent grafts74,76 are then coupled together using aU-shaped adaptor114. TheU-shaped adaptor114 may be constructed in a manner that is similar to the bifurcated outflow cannula64 (FIG. 3), namely, machined from a metallic material and polished, or molded from a polymeric material. Theadaptor114 may include barbs (not shown) located near the ingress and egress openings, in a manner similar to the bifurcated outflow cannula64 (FIG. 3), for attaching the first andsecond stent grafts74,76.Collets116,118 may then be used to secure thestent grafts74,76 to theadaptor114.
• With the circulatory assist system10 (FIG. 1) removed, blood will flow only in accordance with the native path, which was described in detail above. Blood entering the rightsubclavian artery46 will be unable to traverse the portion of the vessel residing between thestent grafts74,76. Instead, blood will flow through thestent grafts74,76 and theU-shaped adaptor114 and then to the axillary artery106 (FIG. 1).
• While the manner of reversing the procedure has been shown with aU-shaped adaptor114 and the rightsubclavian artery46, it would be understood that adaptors having other shapes could also be used in other vascular structures.
• FIGS. 5A and 5B illustrate abifurcated outflow cannula120 having an alternate Y-shaped configuration whereegress channels121,122 are constructed to diverge angularly from the same point distal to theingress channel123. Construction of the alternatebifurcated outflow cannula120 may be in accordance with the methods described previously. Theingress channel123 may include abarb124 for receiving an extension tube94 (FIG. 2); however, it would be understood that theingress channel123 could also couple directly to the output port66 (FIG. 1) of the pump58 (FIG. 1), with or without the use of a collet. To achieve a desired retrograde:radial flow ratio,channel fittings126,128 may be constructed and fitted into theegress channels121,122, respectively. Each channel fitting126,128 will include aninternal lumen130,132 having an internal cross-sectional area for determining the retrograde:radial flow ratio. Thechannel fittings126,128 may includebarbs134,136 for coupling to therespective egress channel121,122. Glue, epoxy, or welding may be used to secure thechannel fittings126,128.Additional barbs138,140 may be included on thechannel fittings126,128 for receiving thestent grafts74,76 (FIG. 1).
• FIGS. 6 and 7 illustrate yet two additional manners of constructing thebifurcated outflow cannula120 where the desired retrograde:radial ratio is selected by the inclusion of a flow selector. The flow selectors inFIG. 6 includeirises141,142 having different inner diameters; the flow selectors inFIG. 7 includerings144,146 also having different inner diameters. While these figures specifically illustrate the flow selectors within theegress channels121,122, it would be understood that the flow selectors could be positioned alternatively, or additionally, in theingress channel123, a position between theingress channel123 and one of theegress channels121,122, or in a combination of these positions. Further, it would be understood that the flow selectors could be positioned in any one of the various embodiments of the bifurcated outflow cannula and can be mixed to suit a particular function.
• FIG. 8 illustrates yet another alternate configuration of thebifurcated outflow cannula148, formed as a t-connector. In this particular configuration, theegress channels150,152 form a 90° angle with respect to theingress channel154 and form a 180° angle therebetween. While the illustrative embodiment is shown with an 80:20 ratio, which was molded or machined, it would be understood that thechannel fittings126,128 ofFIGS. 5A and 5B could alternatively be used. One or more of thechannels150,152,154 may be constructed withbarbs156,158,160 for securing thestent grafts74,76 (FIG. 2) as described previously.
• It would be appreciated by one skilled in the art that the egress channels need not necessarily direct blood into the same arterial vessel.FIG. 9 illustrates another method of using the bifurcatedcannula64 where thefirst stent graft74 enters theaorta38 at the firstvascular incision82aand thesecond stent graft76 enters the leftsubclavian artery40 at the secondvascular incision84a. In this way, the low volume blood flow is directed into the leftsubclavian artery40 for theleft arm162 while the high volume blood flow is directed into theaorta38 for distribution amongst the leftsubclavian artery40, the leftcommon carotid42, and thebrachiocephalic trunk44.FIG. 9 also illustrates theflexible cannula body50 being surgically positioned into theleft atrium18.
• While only a few specific configurations are shown, it would be understood that various arrangements are possible having a single ingress channel and two egress channels.
• While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in some detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The various features of the invention may be used alone or in any combination depending on the needs and preferences of the user. This has been a description of the present invention, along with the preferred methods of practicing the present invention as currently known. However, the invention itself should only be defined by the appended claims.

Claims (17)

1. A bifurcated cannula for directing blood into the arterial system having blood flowing in a first direction, the bifurcated cannula comprising:

an ingress channel for receiving blood flow from a pump;

a first egress channel configured to direct a first portion of the blood from the ingress channel into the arterial system in the first direction; and

a second egress channel configured to direct a second portion of the blood from the ingress channel into the arterial system in a direction that opposes the first direction.

2. The bifurcated cannula ofclaim 1, wherein a cross-sectional area of each of the first and second egress channels determines the first and second portions of blood flowing through the first and second egress channels.

3. The bifurcated cannula ofclaim 2, wherein cross-sectional areas of the first and second egress channels are sized such that the first portion of the blood is less than the second portion of the blood.

4. The bifurcated cannula ofclaim 2, wherein cross-sectional areas of the first and second egress channels are sized such that the first and second portions of the blood are each 50% of the blood flowing through the ingress channel.

5. The bifurcated cannula ofclaim 1, wherein first and second stent grafts are coupled in fluid communication respectively with the first and second egress channels and further adapted to be connected to the arterial system.

6. The bifurcated cannula ofclaim 5, wherein an outer surface of each of the first and second egress channels includes barbs for retaining the respective stent grafts.

7. The bifurcated cannula ofclaim 1, wherein an extension tube is coupled in fluidic communication with the ingress channel and further adapted to be connected to the pump.

8. The bifurcated cannula ofclaim 1, further comprising a flow selector configured to reduce a cross-sectional area of either of the first or second egress channels.

9. The bifurcated cannula ofclaim 8, wherein the flow selector is an iris having two or more pivotable blades.

10. The bifurcated cannula ofclaim 1 further comprising:

a first channel fitting received by the first egress channel, wherein a cross-sectional area of a lumen through the first channel fitting is smaller than a cross-sectional area of the first egress channel.

11. The bifurcated cannula ofclaim 10, further comprising:

a second channel fitting received by the second egress channel, wherein a cross-sectional area of a lumen through the second channel fitting is smaller than a cross-sectional area of the second egress channel.

12. A method of removing the bifurcated cannula ofclaim 1, wherein first and second stent grafts couple the first and second egress channels to the arterial system, the method comprising:

disengaging the pump from the ingress channel;

removing the pump;

removing the bifurcated cannula; and

fluidicly coupling the first and second stent grafts such that the blood flowing in the first direction enters the second stent graft and flows into the first stent graft in the first direction and then flows back into the arterial system in the first direction.

13. A method of directing blood from a pump to the arterial system having blood flowing in a first direction with a bifurcated cannula comprising an ingress channel and first and second egress channels, the method comprising:

directing the blood from the pump into the ingress channel of the bifurcated cannula;

directing a first portion of the blood through the first egress channel and into the arterial system such that the first portion enters the arterial system in the first direction; and

directing a second portion of the blood entering the bifurcated cannula from the ingress channel through the second egress channel and into the arterial system such that the second portion of the blood enters the arterial system in a direction that opposes the first direction.

14. The method according toclaim 13, wherein directing the first and second portions is determined by relative cross-sectional areas of each of the first and second egress channels.

15. The method according toclaim 13, wherein the directing of the first and second portions is determined by a flow selector, wherein the flow selector is configured to reduce a cross-sectional area of either of the first or second egress channels.

16. The method according toclaim 13, further comprising:

coupling the first and second egress channels in fluidic communication respectively to the arterial system by first and second stent grafts.

17. A method of disengaging a circulatory assist system from the arterial system of a patient having blood flowing in a first direction, wherein the circulatory assist system includes a flexible cannula body coupling the left side of the heart of a patient to a pump and a bifurcated cannula comprising an ingress channel for receiving blood from the pump, a first egress channel configured to direct a first portion of the blood from the ingress channel into a first stent graft coupled to the arterial system such that the blood moves in the first direction, and a second egress channel configured to direct a second portion of the blood from the ingress channel into a second stent graft coupled to the arterial system such that the blood moves in a direction that opposes the first direction, the method comprising:

disengaging the first and second egress channels from the first and second stent grafts; and

fluidicly coupling the first and second stent grafts such that the blood flowing in the first direction enters the second stent graft and flows into the first stent graft in the first direction and then flows back into the arterial system in the first direction.

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