1. Field of the Invention
The present invention relates generally to a method of providing extracorporeal access to a patient's vasculature and, more specifically, to accessing a high volume main vessel by first accessing a low volume peripheral vessel.
2. Description of the Related Art
When inserting a cannula into a patient, it may be advantageous to access a vessel having a high volumetric flow capacity. For example, when applying the cardiac assist system described in U.S. Pat. No. 6,685,621, it may be advantageous to locate the inflow and outflow cannulae in one or more high flow vessels. The larger the vessel, the larger the vascular instrument that may be deployed there. Unfortunately, certain high flow vessels, such as those located in the abdominal cavity, are buried deep beneath bodily tissue and organs. Therefore, these vessels are often difficult to access. The difficulty in accessing these vessels is exacerbated by the fact that it is difficult to precisely identify the location of such deeply buried vessels from outside the patient's body.
Traditionally, these vessels have been accessible through a surgical cut down. Such a procedure is highly invasive and traumatic for the patient, requiring a lengthy recovery period including hospitalization. Alternatively, high flow vessels have been accessible through peripheral vessels having lower volumetric flow capacities. For example, to access the descending aorta, a physician may insert a cannula percutaneously into the patient's femoral artery, then advance the cannula upstream into the aorta. The femoral artery is advantageously located subcutaneously near the patient's skin surface, and is easily accessible without the need for a traumatic surgical cut down. Unfortunately, the relatively low volumetric flow capacity of the femoral artery limits the size of the cannula that can be deployed through that access location.
Accordingly, a method of accessing a high flow vessel without causing severe trauma to the patient, while maximizing the size of a cannula to be deployed in the vessel, would be of great benefit to patients undergoing vascular procedures.
The preferred embodiments of the present methods for minimally invasive vascular access have several features, no single one of which is solely responsible for their desirable attributes. Without limiting the scope of these methods as expressed by the claims that follow, their more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of the Preferred Embodiments,” one will understand how the features of the preferred embodiments provide advantages, which include the capability to access high flow vessels without causing severe trauma to the patient, while maximizing the size of a vascular instrument to be deployed in the vessel.
A preferred method of the present invention provides minimally invasive access to a deeply buried target location in a patient's vasculature. Because the target location is buried deep beneath the patient's skin, a relatively large amount of bodily tissue and/or organs lies between a first percutaneous site and the target location. The present inventive method permits relatively easy access to the target location from a second percutaneous site where the vasculature is located relatively close to the skin. The vasculature at the target location includes a vessel segment with a first perimeter that is larger than a second perimeter of a second vessel segment located near the second percutaneous site. The volumetric flow rate at the first vessel segment is significantly higher than at the second vessel segment in some applications. The method comprises the steps of puncturing a patient's skin and vasculature with a needle at the second percutaneous site, inserting a guide wire through the needle and into the vasculature at the second percutaneous site, removing the needle from the vasculature, advancing the guide wire through the vasculature, with the aid of a visualization apparatus, to the target location, advancing a dilator over the guide wire and inserting the dilator into the vasculature at the second percutaneous site, thereby widening an opening in the vasculature at the second percutaneous site, advancing a tunneling device having a cover through the vasculature, with the further aid of the visualization apparatus, along the guide wire from the second percutaneous site to the target location, the tunneling device being configured to be steerable and having a distal point capable of penetrating the vasculature and tissue between the vasculature and the skin, the cover protecting the vasculature as the device travels through the vasculature, piercing the vasculature wall with the tunneling device at the target location and advancing the tunneling device through the vasculature wall and through the patient's tissue, with the further aid of the visualization apparatus, avoiding sensitive bodily structures, to the first percutaneous site, and inserting a cannula through the first percutaneous site, through the patient's tissue, and into the vasculature at the target location.
An alternative method comprises the steps of puncturing a patient's skin with a needle at a percutaneous site above a deeply buried target region of the vasculature, inserting a tunneling device through the patient's skin at the percutaneous site, advancing the tunneling device through the patient's tissue beneath the percutaneous insertion site, with the aid of a visualization apparatus, so as to avoid sensitive bodily structures, to the vasculature, thereby creating a pathway from the percutaneous insertion site to the vasculature proximate the target location, removing the tunneling device from the pathway, advancing a sheath, with the further aid of the visualization apparatus, along the pathway to the vasculature proximate the target location, an end of the sheath including apparatus configured to capture the vasculature, capturing the vasculature with the capturing apparatus and with the further aid of the visualization apparatus, advancing a guide wire through the sheath to the vasculature, with the further aid of the visualization apparatus, advancing a needle along the guide wire to the vasculature, with the further aid of the visualization apparatus, piercing a wall of the vasculature with the needle, and with the further aid of the visualization apparatus, to produce a vascular opening, advancing the guide wire through the vascular opening, with the further aid of the visualization apparatus, and into the vasculature at the target location, removing the needle from the vascular opening, advancing a dilator along the guide wire, with the further aid of the visualization apparatus, and through the vascular opening to widen the opening, advancing a cannula along the guide wire, with the further aid of the visualization apparatus, through the vascular opening, and into the vasculature at the target location.
Various apparatuses described and claimed below can be adapted for one or more aspects of the foregoing methods and variations thereof, including the variations discussed and claimed below. In one embodiment, a tunneling device is provided that permits a clinician to reach a target location of a patient's vasculature from a percutaneous site that is remote from the target location. The target location usually is deeper than subcutaneous. The tunneling device includes an elongate portion configured to pass through the patient's vasculature. The elongate portion has a distal end configured to cut through the vasculature and tissue.
FIGS. 17A-D are schematic views of various tunneling device for use with the present inventive methods of vasculature access.
FIGS. 18A-F are schematic views of tunneling apparatus tips.
FIGS. 19A-B are schematic views of one embodiment of a tunneling device with an extendable cutter.
Turning now to the drawings provided herein, more detailed descriptions of various embodiments of heart assist systems and cannulae for use therewith are provided below. Following this discussion, preferred embodiments of the present methods for minimally invasive vascular access are described, along with various apparatuses that can be used to practice the methods.
I. Heart Assist Systems and Cannulae for Use Therewith
Below, a variety of cannulae and cannula assemblies are described that can be used in connection with a variety of heart assist systems that supplement perfusion. Such systems preferably are extracardiac in nature. In other words, the systems supplement blood perfusion, without the need to interface directly with the heart and aorta. Thus, the systems can be applied without major invasive surgery. The systems also lessen the hemodynamic burden or workload on the heart by reducing afterload, impedence, and/or left ventricular end diastolic pressure and volume (preload). The systems also advantageously increase peripheral organ perfusion and provide improvement in neurohormonal status. As discussed more fully below, the systems can be applied using one or more cannulae, one or more vascular grafts, and a combination of one or more cannulae and one or more vascular grafts. For systems employing cannula(e), the cannula(e) can be applied through multiple percutaneous insertion sites (sometimes referred to herein as a multi-site application) or through a single percutaneous insertion site (sometimes referred to herein as a single-site application).
A. Heart Assist Systems and Methods Employing Multi-Site Application
With reference to
The heart assist system 10 comprises a pump 32, having an inlet 34 and an outlet 36 for connection of conduits thereto. The pump 32 preferably is a rotary pump, either an axial type or a centrifugal type, although other types of pumps may be used, whether commercially-available or customized. The pump 32 preferably is sufficiently small to be implanted subcutaneously and preferably extrathoracically, for example in the groin area of the patient 12, without the need for major invasive surgery. Because the heart assist system 10 is an extracardiac system, no valves are necessary. Any inadvertent backflow through the pump 32 and/or through the inflow conduit would not harm the patient 12.
Regardless of the style or nature chosen, the pump 32 is sized to generate blood flow at subcardiac volumetric rates, less than about 50% of the flow rate of an average healthy heart, although flow rates above that may be effective. Thus, the pump 32 is sized and configured to discharge blood at volumetric flow rates anywhere in the range of 0.1 to 3 liters per minute, depending upon the application desired and/or the degree of need for heart assist. For example, for a patient experiencing advanced congestive heart failure, it may be preferable to employ a pump that has an average subcardiac rate of 2.5 to 3 liters per minute. In other patients, particularly those with minimal levels of heart failure, it may be preferable to employ a pump that has an average subcardiac rate of 0.5 liters per minute or less. In yet other patients it may be preferable to employ a pump that is a pressure wave generator that uses pressure to augment the flow of blood generated by the heart.
In one embodiment, the pump 32 is a continuous flow pump that superimposes continuous blood-flow on the pulsatile aortic blood-flow. In another embodiment, the pump 32 has the capability of synchronous actuation; i.e., it may be actuated in a pulsatile mode, either in copulsating or counterpulsating fashion.
For copulsating action, it is contemplated that the pump 32 would be actuated to discharge blood generally during systole, beginning actuation, for example, during isovolumic contraction before the aortic valve opens or as the aortic valve opens. The pump 32 would be static while the aortic valve is closed following systole, ceasing actuation, for example, when the aortic valve closes.
For counterpulsating actuation, it is contemplated that the pump 32 would be actuated generally during diastole, ceasing actuation, for example, before or during isovolumic contraction. Such an application would permit and/or enhance coronary blood perfusion. In this application, it is contemplated that the pump 32 would be static during the balance of systole after the aortic valve is opened, to lessen the burden against which the heart must pump. The aortic valve being open encompasses the periods of opening and closing, wherein blood is flowing therethrough.
It should be recognized that the designations copulsating and counterpulsating are general identifiers and are not limited to specific points in the patient's heart cycle when the pump 32 begins and discontinues actuation. Rather, they are intended to generally refer to pump actuation in which the pump 32 is actuating, at least in part, during systole and diastole, respectively. For example, it is contemplated that the pump 32 might be activated to be out of phase from true copulsating or counterpulsating actuation described herein, and still be synchronous, depending upon the specific needs of the patient or the desired outcome. One might shift actuation of the pump 32 to begin prior to or after isovolumic contraction or to begin before or after isovolumic relaxation.
Furthermore, the pulsatile pump may be actuated to pulsate asynchronously with the patient's heart. Typically, where the patient's heart is beating irregularly, there may be a desire to pulsate the pump 32 asynchronously so that the perfusion of blood by the heart assist system 10 is more regular and, thus, more effective at oxygenating the organs. Where the patient's heart beats regularly, but weakly, synchronous pulsation of the pump 32 may be preferred.
The pump 32 is driven by a motor 40 and/or other type of drive means and is controlled preferably by a programmable controller 42 that is capable of actuating the pump 32 in pulsatile fashion, where desired, and also of controlling the speed or output of the pump 32. For synchronous control, the patient's heart would preferably be monitored with an EKG in which feedback would be provided to the controller 42. The controller 42 is preferably programmed through external means, such as, for example, RF telemetry circuits of the type commonly used within implantable pacemakers and defibrillators. The controller may also be autoregulating to permit automatic regulation of the speed, and/or regulation of the synchronous or asynchronous pulsation of the pump 32, based upon feedback from ambient sensors monitoring parameters, such as pressure or the patient's EKG. It is also contemplated that a reverse-direction pump be used, if desired, in which the controller is capable of reversing the direction of either the drive means or the impellers of the pump. Such a pump might be used where it is desirable to have the option of reversing the direction of circulation between two blood vessels.
Power to the motor 40 and the controller 42 may be provided by a power source 44, such as a battery, that is preferably rechargeable by an external induction source (not shown), such as an RF induction coil that may be electromagnetically coupled to the battery to induce a charge therein. Alternative power sources are also possible, including a device that draws energy directly from the patient's body; e.g., the patient's muscles, chemicals or heat. The pump can be temporarily stopped during recharging with no appreciable life threatening effect, because the system only supplements the heart, rather than substituting for the heart.
While the controller 42 and power source 44 are preferably pre-assembled to the pump 32 and implanted therewith, it is also contemplated that the pump 32 and motor 40 be implanted at one location and the controller 42 and the power source 44 be implanted in a separate location. In one alternative arrangement, the pump 32 may be driven externally through a percutaneous drive line or cable, as shown in
The inlet 34 of the pump 32 is preferably connected to an inflow conduit 50 and an outflow conduit 52 to direct blood flow from one peripheral blood vessel to another. The conduits 50, 52 preferably are flexible conduits, as discussed more fully below. The conduits 50, 52 are coupled with the peripheral vessels in different ways in various embodiments of the heart assist system 10. As discussed more fully below, at least one of the conduits 50, 52 can be connected to a peripheral vessel, e.g., as a graft, using an anastomosis connection, and at least one of the conduits 50, 52 can be coupled with the same or another vessel via insertion of a cannula into the vasculature. Also, more than two conduits are used in some embodiments, as discussed below.
The inflow and outflow conduits 50, 52 may be formed from Dacron, Hemashield, Gortex, PVC, polyurethane, PTFE, ePTFE, nylon, or PEBAX materials, although other synthetic materials may be suitable. The inflow and outflow conduits 50, 52 may also comprise biologic materials or pseudobiological (hybrid) materials (e.g., biologic tissue supported on a synthetic scaffold). The inflow and outflow conduits 50, 52 are preferably configured to minimize kinks so blood flow is not meaningfully interrupted by normal movements of the patient or compressed easily from external forces. In some cases, the inflow and/or outflow conduits 50, 52 may come commercially already attached to the pump 32. Where it is desired to implant the pump 32 and the conduits 50, 52, it is preferable that the inner diameter of the conduits 50, 52 be less than 25 mm, although diameters slightly larger may be effective.
In one preferred application, the heart assist system 10 is applied in an arterial-arterial fashion; for example, as a femoral-axillary connection, as is shown in
Where the conduit 50 is at least partially extracorporeal, the inflow cannula 60 also may be inserted through a surgical opening (e.g., as shown in
In another embodiment, the inflow conduit 50 is connected to the first blood vessel via an end-to-side anastomosis, rather than via the inflow cannula 60. The inflow conduit 50 could also be coupled with the first blood vessel via a side-to-side anastomosis connection mid-stream of the conduit, where the inflow conduit connects at its second end to an additional blood vessel or at another location on the same blood vessel (neither shown). Further details of these arrangements and other related applications are described in U.S. application Ser. No. 10/289,467, filed Nov. 6, 2002, the entire contents of which is hereby incorporated by reference in its entirety and made a part of this specification.
In another embodiment, the outflow conduit 52 also is coupled with the second blood vessel via a cannula, as shown in
Preferably, the heart assist system 10 is applied to the peripheral or non-primary blood vessels subcutaneously; e.g., at a shallow depth just below the skin or first muscle layer so as to avoid major invasive surgery. It is also preferred that the heart assist system 10 be applied extrathoracically to avoid the need to invade the patient's chest cavity. Where desired, the entire heart assist system 10 may be implanted within the patient 12, either extravascularly, e.g., as in
In the case of an extravascular application, the pump 32 may be implanted, for example, into the groin area, with the inflow conduit 50 fluidly connected subcutaneously to, for example, the femoral artery 26 proximate the pump 32. The outflow conduit would be tunneled subcutaneously through to, for example, the left subclavian artery 24. In an alternative arrangement, the pump 32 and associated drive and controller could be temporarily fastened to the exterior skin of the patient, with the inflow and outflow conduits 50, 52 connected percutaneously. In either case, the patient may be ambulatory without restriction of tethered lines.
While the heart assist system 10 and other heart assist systems described herein may be applied to create an arterial-arterial flow path, given the nature of the heart assist systems, i.e., supplementation of circulation to meet organ demand, a venous-arterial flow path may also be used. For example, with reference to
In those venous-arterial cases where the inflow is connected to a vein and the outflow is connected to an artery, the pump 32 is preferably sized to permit flow sufficiently small so that oxygen-deficient blood does not rise to unacceptable levels in the arteries. The connections to the non-primary veins could be by one or more of the approaches described above for connecting to a non-primary artery. The extracardiac assist system could also be applied as a venous-venous flow path, wherein the inflow and outflow are connected to separate peripheral veins. In addition, an alternative embodiment comprises two discrete pumps and conduit arrangements, one being applied as a venous-venous flow path, and the other as an arterial-arterial flow path.
When venous blood is mixed with arterial blood, either at the inlet of the pump or at the outlet of the pump, the ratio of venous blood to arterial blood is preferably controlled to maintain an arterial saturation of a minimum of 80% at the pump inlet or outlet. Arterial saturation can be measured and/or monitored by pulse oximetry, laser doppler, colorimetry or other methods used to monitor blood oxygen saturation. The venous blood flow into the system can then be controlled by regulating the amount of blood allowed to pass through the conduit from the venous-side connection.
In one arrangement, all four conduits are connected to peripheral arteries. In another arrangement, one or more of the conduits could be connected to veins. In the arrangement of
The connections of any or all of the conduits of the system 110 to the blood vessels may be via an anastomosis connection or via a connector, as described below in connection with
Where an anastomosis connection is not desired, a connector may be used to connect at least one of the inflow conduit and the outflow conduit to a peripheral blood vessel. With reference to
Other types of connectors having other configurations are contemplated that may avoid the need for an anastomosis connection or that permit connection of the conduit(s) to the blood vessel(s). For example, it is contemplated that an L-shaped connector be used if it is desired to withdraw blood more predominantly from one direction of a peripheral vessel or to direct blood more predominantly into a peripheral vessel. Referring to
The L-shaped connector 278 has an inlet port 280 at a proximal end and an outlet port 282 through which blood flows into the inflow conduit 250. The L-shaped connector 278 also has an arrangement of holes 284 within a wall positioned at a distal end opposite the inlet port 280 so that some of the flow drawn into the L-shaped connector 278 is diverted through the holes 284, particularly downstream of the L-shaped connector 278, as in this application. A single hole 284 in the wall could also be effective, depending upon size and placement. The L-shaped connector 278 may be a deformable L-shaped catheter percutaneously applied to the blood vessel or, in an alternative embodiment, be connected directly to the walls of the blood vessel for more long term application. By directing some blood flow downstream of the L-shaped connector 278 during withdrawal of blood from the vessel, ischemic damage downstream from the connector may be avoided. Such ischemic damage might otherwise occur if the majority of the blood flowing into the L-shaped connector 278 were diverted from the blood vessel into the inflow conduit 252. It is also contemplated that a connection to the blood vessels might be made via a cannula, wherein the cannula is implanted, along with the inflow and outflow conduits.
One advantage of discrete connectors manifests in their application to patients with chronic CHF. A connector eliminates a need for an anastomosis connection between the conduits 250, 252 and the peripheral blood vessels where it is desired to remove and/or replace the system more than one time. The connectors could be applied to the first and second blood vessels semi-permanently, with an end cap applied to the divergence for later quick-connection of the cardiac assist system to the patient. In this regard, a patient might experience the benefit of the heart assist systems described herein periodically, without having to reconnect and redisconnect the conduits 250, 252 from the blood vessels via an anastomosis procedure each time. Each time it is desired to implement any of the embodiments of the heart assist system, the end caps would be removed and a conduit attached to the connector(s) quickly.
In the preferred embodiment of the connector 268, the divergence 276 is oriented at an acute angle significantly less than 90 degrees from the axis of the T-shaped fitting 270, as shown in
With or without a connector, with blood flow directed proximally toward the aorta 16, the result may be concurrent flow down the descending aorta, which will result in the reduction of afterload, impedence, and/or reducing left ventricular end diastolic pressure and volume (preload). Thus, the heart assist systems described herein may be applied so to reduce the afterload on the patient's heart, permitting at least partial if not complete CHF recovery, while supplementing blood circulation. Concurrent flow depends upon the phase of operation of the pulsatile pump and the choice of second blood vessel to which the outflow conduit is connected.
A partial external application of the heart assist systems may be appropriate where a patient with heart failure is suffering an acute decompensation episode; i.e., is not expected to survive long, or in the earlier stages of heart failure (where the patient is in New York Heart Association Classification (NYHAC) functional classes II or III). With reference to
The pump 332 has an inflow conduit 350 and an outflow conduit 352 associated therewith for connection to two non-primary blood vessels. The inflow conduit 350 has a first end 356 and a second end 358 wherein the second end 358 is connected to a first non-primary blood vessel (e.g., femoral artery 26) by way of an inflow cannula 380. The inflow cannula 380 has a first end 382 sealably connected to the second end 358 of the inflow conduit 350. The inflow cannula 380 also has a second end 384 that is inserted through a surgical opening 386 or an introducer sheath (not shown) and into the blood vessel (e.g., the left femoral artery 26).
Similarly, the outflow conduit 352 has a first end 362 and a second end 364 wherein the second end 364 is connected to a second non-primary blood vessel (e.g., the left subclavian artery 24, as shown in
As shown in
An alternative variation of the embodiment of
Specific methods of applying this alternative embodiment may further comprise coupling the inflow conduit 352 upstream of the outflow conduit 350 (as shown in
A means for minimizing the loss of thermal energy from the patient's blood may be provided where any of the heart assist systems described herein are applied extracorporeally. Such means for minimizing the loss of thermal energy may comprise, for example, a heated bath through which the inflow and outflow conduits pass or, alternatively, thermal elements secured to the exterior of the inflow and outflow conduits. Referring to
If desired, the cardiac assist system may further comprise a reservoir that is either contained within or in fluid communication with the inflow conduit. This reservoir is preferably made of materials that are nonthrombogenic. Referring to
As explained above, one of the advantages of several embodiments of the heart assist system is that such systems permit the patient to be ambulatory. The systems may be designed to be portable, so the patient may carry the system. Referring to
B. Heart Assist Systems and Methods Employing Single-Site Application
As discussed above, heart assist systems can be applied to a patient through a single cannulation site. Such single-site systems can be configured with a pump located outside the vasculature of a patient, e.g., as extravascular pumping systems, inside the vasculature of the patient, e.g., as intravascular systems, or a hybrid thereof, e.g., partially inside and partially outside the vasculature of the patient.
1. Single-Site Application of Extravascular Pumping Systems
In one embodiment, the multilumen cannula 460 includes a first lumen 466 and a second lumen 468. The first lumen 466 extends from a proximal end 470 of the multilumen cannula 460 to a first distal end 472. The second lumen 468 extends from the proximal end 470 to a second distal end 474. In the illustrated embodiment, the second end 458 of the inflow conduit 450 is connected to the first lumen 466 of the multilumen cannula 460 and the second end 464 of the outflow conduit 452 is connected to the second lumen 468 of the multilumen cannula 460.
Where there is a desire for the patient 12 to be ambulatory, the multilumen cannula 460 preferably is made of material sufficiently flexible and resilient to permit the patient 12 to comfortably move about while the multilumen cannula 460 is indwelling in the patient's blood vessels without causing any vascular trauma.
The application shown in
The pump 432 draws blood from the patient's vascular system in the area near the distal end 472 and into the lumen 466. This blood is further drawn into the lumen of the conduit 450 and into the pump 432. The pump 432 then expels the blood into the lumen of the outflow conduit 452, which carries the blood into the lumen 468 of the multilumen cannula 460 and back into the patient's vascular system in the area near the distal end 474.
The outflow port 492 may be situated within, for example, a mesenteric artery 494 such that blood flow results from the left femoral artery 26 to the mesenteric artery 494. The blood could discharge, for example, directly into the descending aorta proximate an arterial branch, such as the renal arteries, the left subclavian artery, or directly into the peripheral mesenteric artery 494, as illustrated in
Additional details of the multilumen cannula 460 may be found in U.S. patent application Ser. No. 10/078,283, filed Feb. 14, 2002, entitled A MULTILUMEN CATHETER FOR MINIMIZING LIMB ISCHEMIA and in U.S. patent application Ser. No. 10/706,346, filed Nov. 12, 2003, entitled CANNULAE HAVING REDIRECTING TIP, which are hereby expressly incorporated by reference in their entirety and made a part of this specification.
The vascular graft 550 has a first end 554 and a second end 556. The first end 554 is sized and configured to couple to a non-primary blood vessel 558 subcutaneously to permit application of the extracardiac pumping system 510 in a minimally-invasive procedure. In one application, the vascular graft conduit 550 is configured to couple to the blood vessel 558 via an anastomosis connection.
The second end 556 of the vascular graft 550 is fluidly coupled to the pump 532 to conduct blood between the non-primary blood vessel 558 and the pump 532. In the embodiment shown, the second end 556 is directly connected to the pump 532, but, as discussed above in connection with other embodiments, intervening fluid conducting elements may be interposed between the second end 556 of the vascular graft 550 and the pump 532. Examples of arrangements of vascular graft conduits may be found in U.S. application Ser. No. 09/780,083, filed Feb. 9, 2001, entitled EXTRA-CORPOREAL VASCULAR CONDUIT, which is hereby incorporated by reference in its entirety and made a part of this specification.
In the illustrated embodiment, the insertion site 560 is configured to receive the cannula 562 therethrough in a sealable manner. In another embodiment, the insertion site 560 is configured to receive the outflow conduit 552 directly. The cannula 562 includes a first end 564 sized and configured to be inserted through the insertion site 560, through the cannula 550, and through the non-primary blood vessel 558. The conduit 552 has a second end 566 fluidly coupled to the pump 532 to conduct blood between the pump 532 and the blood vessel 558.
The extracardiac pumping system 510 can be applied to a patient, as shown in
2; Single-Site Application of Intravascular Pumping Systems
The impeller blade(s) 616 of the pumping means 614 of this embodiment may be driven in one of a number of ways known to persons of ordinary skill in the art. In the embodiment shown in
Variations of the intravascular embodiment of
In one embodiment, the pumping means 644 also includes a conduit 652 in which the pump 646 is housed. The conduit 652 may be relatively short, as shown, or may extend well within the designated blood vessel or even into an adjoining or remote blood vessel at the inlet end, at the outlet end, or at both the inlet and outlet. The intravascular extracardiac system 642 may further comprise an additional parallel-flow conduit, as discussed below in connection with the system of
The intravascular extracardiac system 642 may further comprise inflow and/or outflow conduits or cannulae (not shown) fluidly connected to the pumping means 644, e.g., to the inlet and outlet of pump 646. Any suitable conduit or cannula can be employed. For example, a cannula defining a lumen with an inner size that increases distally could be coupled with an intravascular extracardiac system.
In another embodiment, an intravascular pumping means 644 may be positioned within one lumen of a multilumen catheter so that, for example, where the catheter is applied at the left femoral artery, a first lumen may extend into the aorta proximate the left subclavian and the pumping means may reside at any point within the first lumen, and the second lumen may extend much shorter just into the left femoral or left iliac. Such a system is described in greater detail in U.S. application Ser. No. 10/078,283, incorporated by reference herein above.
The intravascular extracardiac system described herein may be inserted into a patient's vasculature by any means known to those of ordinary skill, or by any obvious variant thereof. In one method of use, such a system is temporarily housed within a catheter that is inserted percutaneously, or by surgical cutdown, into a non-primary blood vessel and advanced through to a desired location. The catheter preferably is then withdrawn away from the system so as not to interfere with operation of the system, but to still permit the withdrawal of the system from the patient when desired. Further details of intravascular pumping systems may be found in U.S. patent application Ser. No. 10/686,040, filed Oct. 15, 2003, which is hereby incorporated by reference herein in its entirety.
C. Potential Enhancement of Systemic Arterial Blood Mixing
An advantage of the cardiac assist systems described above is the potential to enhance mixing of systemic arterial blood, particularly in the aorta. Such enhanced mixing ensures the delivery of blood with higher oxygen-carrying capacity to organs supplied by arterial side branches off of the aorta. A method of enhancing mixing using the cardiac assist systems described above preferably includes taking steps to assess certain parameters of the patient and then to determine the minimum output of the pump that, when combined with the heart output, ensures turbulent flow in the aorta, thereby enhancing blood mixing.
Blood flow in the aortic arch during normal cardiac output may be characterized as turbulent in the end systolic phase. Turbulence in a flow of fluid enhances the uniform distribution of particles within the fluid. It is believed that turbulence in the descending aorta enhances the homogeneity of blood cell distribution in the aorta. Laminar flow of viscous fluids leads to a higher concentration of particulate in the central portion of the flow. It is believed that, in low flow states such as that experienced during heart failure, there is reduced or inadequate mixing of blood cells leading to a lower concentration of nutrients at the branches of the aorta to peripheral organs and tissues. As a result, the blood flowing into branch arteries off of the aorta will likely have a lower hematocrit, especially that flowing into the renal arteries, the celiac trunk, the spinal arteries, and the superior and inferior mesenteric arteries, because these branches draw from the periphery of the aorta. The net effect of this phenomenon is that the blood flowing into these branch arteries has a lower oxygen-carrying capacity, because oxygen-carrying capacity is directly proportional to both hematocrit and the fractional O2 saturation of hemoglobin. Under those circumstances, these organs may experience ischemia-related pathology.
The phenomenon of blood streaming in the aorta, and the resultant inadequate mixing of blood resulting in central lumenal concentration of blood cells, is believed to occur when the Reynolds number (NR) for the blood flow in the aorta is below 2300. To help ensure that adequate mixing of blood will occur in the aorta to prevent blood cells from concentrating in the center of the lumen, a method of applying the cardiac assist systems described above to a patient may also include steps to adjust the output of the pump to attain turbulent flow within the descending aorta upstream of the organ branches; i.e., flow exhibiting a peak Reynolds number of at least 2300 within a complete cycle of systole and diastole. Because flow through a patient is pulsatile in nature, and not continuous, consideration is preferably given to how frequently the blood flow through the aorta has reached a certain desired velocity and, thus, a desired Reynolds number. The method contemplated herein, therefore, may also include the step of calculating the average Womersley number (NW), which is a function of the frequency of the patient's heart beat. Preferably, a peak Reynolds number of at least 2300 is attained when the corresponding Womersley number for the same blood flow is approximately 6 or above.
More specifically, the method may comprise calculating the Reynolds number for the blood flow in the descending aorta by determining the blood vessel diameter and both the velocity and viscosity of the fluid flowing through the aorta. The Reynolds number may be calculated pursuant to the following equation:
where: V=the velocity of the fluid; d=the diameter of the vessel; and υ=the viscosity of the fluid. The velocity of the blood flowing through the aorta is a function of the cross-sectional area of the aorta and the volume of flow therethrough, the latter of which is determined both by the patient's own cardiac output and by the output of the extra cardiac pump. Velocity may be calculated by the following equation:
where Q=the volume of blood flowing through the blood vessel, e.g., the aorta, per unit time; and r=the radius of the vessel. If the relationship between the pump output and the velocity is already known or independently determinable, the volume of blood flow Q may consist only of the patient's cardiac output, with the knowledge that that output will be supplemented by the subcardiac pump. If desired, however, the cardiac assist system can be implemented and applied to the patient first, before calculating Q, which would consist of the combination of cardiac output and the pump output.
The Womersley number may be calculated as follows:
where r is the radius of the vessel being assessed, ω is the frequency of the patient's heartbeat, and υ=the viscosity of the fluid. For a peak Reynolds number of at least 2300, a Womersley number of at least 6 is preferred, although lower values, such as 5, would also be acceptable.
By determining (i) the viscosity of the patient's blood, which is normally about 3.0 mm2/sec (kinematic viscosity), (ii) the cardiac output of the patient, which of course varies depending upon the level of CHF and activity, and (iii) the diameter of the patient's descending aorta, which varies from patient to patient but is about 21 mm for an average adult, one can determine the flow rate Q that would result in a velocity through the aorta necessary to attain a Reynolds number of at least 2300 at its peak during the patient's heart cycle. Based upon that determination of Q, one may adjust the output of the pump to attain the desired turbulent flow characteristic through the aorta, enhancing mixing of the blood therethrough.
One may use ultrasound (e.g., echocardiography or abdominal ultrasound) to measure the diameter of the aorta, which is relatively uniform in diameter from its root to the abdominal portion of the descending aorta. One may measure cardiac output using a thermodilution catheter or other techniques known to those of skill in the art. Finally, one may measure viscosity of the patient's blood by using known methods; for example, using a capillary viscosimeter. In many cases, the above methods will provide a basis to more finely tune the system to more optimally operate the system to the patient's benefit. Other methods may include steps to assess other patient parameters that enable a person of ordinary skill in the art to optimize the cardiac assist system to ensure adequate mixing within the vascular system of the patient.
Alternative methods that provide the benefits discussed herein include the steps of, prior to applying a shape change therapy, applying a blood supplementation system (such as one of the many examples described herein) to a patient, whereby the methods are designed to improve the ability to reduce the size and/or wall stress of the left ventricle, or both ventricles, thus reducing ventricular loading. Specifically, one example of such a method comprises the steps of providing a pump configured to pump blood at subcardiac rates, providing inflow and outflow conduits configured to fluidly communicate with non-primary blood vessels, fluidly coupling the inflow conduit to a non-primary blood vessel, fluidly coupling the outflow conduit to the same or different (primary or non-primary) blood vessel and operating the subcardiac pump in a manner, as described herein, to reduce the load on the heart, wherein the fluidly coupling steps may comprise anastomosis, percutaneous canalization, positioning the distal end of one or both conduits within the desired terminal blood vessel or any combination thereof. The method further comprises, after sufficient reduction in ventricular loading, applying a shape change therapy in the form of, for example, a cardiac reshaping device, such as those referred to herein, or others serving the same or similar function, for the purpose of further reducing the size of and/or wall stress on one or more ventricles and, thus, the heart, and/or for the purpose of maintaining the patient's heart at a size sufficient to enhance recovery of the patient's heart.
II. Method of Percutaneously Accessing High Flow Vessels
A variety of methods are discussed below for accessing a segment of the vasculature of a patient that is deeply buried, e.g., beneath organs and other soft tissues. The deeply buried segment of the vasculature to be accessed generally has a larger perimeter than segments of the vasculature that are close to the skin, e.g., segments that can be accessed by conventional percutaneous techniques. These vessel segments are at least in this sense relatively large. The deeply buried vessel segment generally has a relatively high flow capacity due to its size. These methods can involve accessing such vessels by way of peripheral vessels and methods of directly accessing high flow vessels from a percutaneous site above the high flow vessel.
A. Accessing Large Perimeter Vessel Segments From Other Vessel Segments
In a class of methods, a clinician is able to access a deeply buried, relatively large (e.g., high volume flow) portion of the vasculature for, among other applications, supplementing blood flow in a manner described herein or otherwise. To avoid the need for surgical cut-down, but without sacrificing the use of a high volume flow catheter, one method of the present invention comprises accessing the deeply buried target vasculature site with a catheter directed through a proximate first percutaneous site by way of a second percutaneous site. In that regard, one method comprises the step of puncturing the patient's skin and vasculature with a needle at the second percutaneous site remote from the target location and then inserting a guide wire through the needle and into the vasculature at the second percutaneous site. The needle is then removed from the vasculature and the guide wire is advanced through the vasculature to the target location. To ensure that the guide wire reaches the target location, and to follow the progress of the guide wire along the way, the guide wire may be tracked with the aid of visualization apparatus. For example, the visualization apparatus may comprise a fiber-optic camera, ultrasound apparatus or fluoroscopy apparatus. Those of skill in the art will appreciate that other visualization apparatus could be used in addition to, or instead of, the examples listed above.
The needle produces relatively small openings in the skin and in the vasculature at the second percutaneous site. Therefore, it is often advantageous to widen these openings using one or more dilators. To do so, at least one dilator may be advanced over the guide wire and inserted into the vasculature at the second percutaneous site. The dilator widens the openings in the vasculature and the skin at the second percutaneous site. The openings may be widened a little bit at a time by using successively larger dilators. This process is known as step dilation, and is well known by those of skill in the art.
When the openings in the vasculature and the skin at the second percutaneous site are sufficiently wide, a tunneling device is advanced along the guide wire and into the vasculature. For example, the tunneling device may comprise a tunneling catheter having a distal tip. As discussed further below, the distal tip can have a structure configured to pierce a portion of the vasculature of the patient, e.g., a vessel wall. As discussed further below, the distal tip or vasculature piercing structure may be covered, e.g., by being at least temporarily retracted within a portion of the catheter. In some embodiments, a cover may be provided that is retractable to expose the distal tip or vasculature piercing structure. In one method, the tunneling device is advanced along the guide wire through the vasculature to the target location. For this step, visualization apparatus may again be used.
Once the tunneling device distal tip reaches the target location, a cover is removed, if one has been provided. In some embodiments, the cover can comprise a sheath that can be moved relative to the distal tip or relative to the vasculature piercing structure to expose or to release the tip or structure. The sheath extends over at least a portion of the outer surface of the distal tip or vasculature piercing structure in some embodiments. The sheath is a structure that prevents harmful interaction between the vasculature and the distal tip or vasculature piercing structure prior to intended piercing of a vessel wall at the target location. In other embodiments, the distal tip or vasculature piercing structure can be configured to be extended distally to expose a portion of the tunneling device, e.g., the distal tip or vasculature piercing structure, adjacent to the target location. The distal tip of the tunneling device is then manipulated to pierce the vasculature wall at the target location. The tunneling device is advanced through the vasculature wall and through the patient's tissue to the first percutaneous site. During the tunneling process, any suitable technique may be used to prevent excess bleeding at the target location or in the intervening tissue. In order to avoid sensitive bodily structures, a visualization apparatus may again be used.
The tunneling device provides a path from the first percutaneous site to the target location. A guidewire may also be used to telegraph the pathway. After the pathway has been created, the tunneling device may be removed from the pathway. If the tunneling device has been removed from the pathway, then a sheath can be advanced along the pathway to the vasculature proximate the target location. However, if the tunneling device has been left in place, then a sheath is advanced over the tunneling device to the vasculature proximate the target location. A visualization apparatus may be employed for these steps.
A distal end of the sheath preferably includes an apparatus that is configured to capture the vasculature. For example, at the distal end of the sheath, opposing side walls may include first and second arcuate cutout portions. The cutouts are adapted to receive the vessel, such that the vessel runs substantially perpendicular to a longitudinal axis of the sheath, and the cutouts at least partially surround the vessel. With the aid of the capturing apparatus, the vasculature is captured. Visualization apparatus may be employed to complete this step. If the tunneling device is still resident within the sheath, it can be removed at this point. A cannula can be passed to the target location through the sheath or tunneling device or over the guide wire.
The tunneling device, sheath, and/or the guide wire may thus be used to guide a cannula through the first percutaneous site, through the patient's tissue, and to or into the vasculature at the target location. The method described above may be used to access any of a wide variety of target locations. For example, the target location may be the abdominal aorta or the vena cava. By using the method described herein, these targets may be accessed through any of a wide variety of second percutaneous sites. For example, the second percutaneous site may be located at the axillary artery, the iliac artery of vein, the femoral artery or vein, the subclavian artery or vein, the common carotid artery, the brachiocephalic artery, the great saphenous vein, the internal or external jugular vein, or the basilic vein.
B. Accessing Large Perimeter Vessel Segments from Above a Target Location
If desired, an alternate application of the present inventive method comprises puncturing a patient's skin with a needle at the first percutaneous site; inserting a tunneling device through the patient's skin at the percutaneous site; advancing the tunneling device through the patient's tissue beneath the percutaneous insertion site, with the aid of a visualization apparatus, so as to avoid sensitive bodily structures, to the vasculature, thereby creating a pathway from the percutaneous insertion site to the vasculature proximate the target location; removing the tunneling device from the pathway; advancing a sheath, with the further aid of the visualization apparatus, along the pathway to the vasculature proximate the target location, an end of the sheath including apparatus configured to capture the vasculature; capturing the vasculature with the capturing apparatus and with the further aid of the visualization apparatus; advancing a guide wire through the sheath to the vasculature, with the further aid of the visualization apparatus; advancing a needle along the guide wire to the vasculature, with the further aid of the visualization apparatus; piercing a wall of the vasculature with the needle, and with the further aid of the visualization apparatus, to produce a vascular opening; advancing the guide wire through the vascular opening, with the further aid of the visualization apparatus, and into the vasculature at the target location; removing the needle from the vascular opening; advancing a dilator along the guide wire, with the further aid of the visualization apparatus, and through the vascular opening to widen the opening; and advancing a cannula along the guide wire, with the further aid of the visualization apparatus, through the vascular opening, and into the vasculature at the target location.
As discussed above, one variation involves accessing a large or relatively large perimeter vessel (e.g., a relatively high flow vessel) from above the target location. This technique is sometimes referred to herein as accessing the target location directly. Here, “directly” and “direct access” are broad terms and they include access a vessel or a vessel segment at a target location without the need previously to insert a guide wire, tunneling device, or other structure into the vasculature at another location or through another vessel segment. These and similar terms also include techniques that create a pathway primarily through non-vascular tissues, as discussed below.
Direct access methods can be facilitated by securing the vasculature at the target location. In one technique, the sheath with cutout portions adapted to receive a vessel, which is discussed above, is used to secure the vasculature at a target location. Once the vasculature has been secured, a guide wire is advanced through the sheath to the vasculature in one technique. A needle is then advanced along the guide wire to the vasculature. The needle pierces a wall of the vasculature. Visualization apparatus may be used to complete these steps. The needle produces a vascular opening, through which the guide wire is advanced into the vasculature at the target location. When the needle is removed from the vascular opening, the vascular opening tends to close up and assume the size of the guide wire. Therefore, in order to widen the vascular opening, a dilator may be advanced along the guide wire and through the vascular opening. A series of progressively larger dilators may be advanced through the vascular opening until it achieves the desired size. Once the vascular opening is large enough, a cannula is advanced along the guide wire, through the vascular opening, and into the vasculature at the target location. At each of the above steps, a visualization apparatus may be employed.
In the above methods, the tunneling device may comprise a removable core with a tunneling tip. With such a tunneling device, once the device reaches the vasculature at the target location, the capturing apparatus is extended from the tunneling device to capture the vasculature. The core is then removed from the tunneling device, leaving behind a sheath. The remaining steps may proceed as described above.
In performing the above methods, one of a number of possible tunneling devices may be used, with optional features that may enhance operation. The tunneling device preferably includes a distal end that is configured to penetrate the vasculature and tissue between the target vasculature site and the first percutaneous site. For example, the distal end may include a simple dissection tip, a trocar-type tip, a hollow catheter with an extendable cutter, a blunt dissection tip, a laser tip, an RF tip, an electrosurgical tip, or an ultrasound tip. If the distal tip of the tunneling device is sharp, then in order to prevent damage to the vasculature, a removable cover may shield the distal tip as the tunneling device travels through the vasculature.
Referring to
If desired, the tunneling device 700 may be configured to be steerable by the clinician. Referring to
Referring to FIGS. 22A-B, an alternative tunneling device 800 comprises a tube 810 with a high temperature insulating layer thereon. If desired, a lubricious coating 830 may be applied thereto. The tube 810 supports at a distal end 820 an electrode 840 of one of many possible configurations to burn away tissue, to pierce the vasculature, and to cut through tissue while tunneling. The electrode 840 may be retractable. The tunneling device 800 may also be steerable. Referring to
The present method may be used to reach a target location that is not a treatment site at which the vascular procedure is desired to be performed. In such a case, the target location may be selected because it is a location at which a relatively large vascular instrument may be inserted and then advanced intravascularly to a treatment location. For example, the vascular instrument may be a cannula, and the target location may be in the iliac artery, while the treatment location is in the aortic arch. The cannula may thus be inserted into the iliac artery through the first percutaneous site, and then advanced to the aortic arch to perform the desired treatment. Additional examples of treatment locations include the abdominal aorta, the axillary artery or vein, and the inferior or superior vena cava.
The above steps illustrate some examples of the present inventive methods and present a description of the best mode contemplated for carrying out the present methods for minimally invasive vascular access, and of the manner and process of performing them, in such full, clear, concise, and exact terms as to enable any person skilled in the art to which they pertain to practice these methods. These methods are, however, susceptible to modifications and alternate apparatus from that discussed above that are fully equivalent. Consequently, these methods are not limited to the particular embodiments disclosed. On the contrary, these methods cover all modifications and alternate constructions coming within the spirit and scope of the methods as generally expressed by the following claims, which particularly point out and distinctly claim the subject matter of the methods.