WO2000035515A1

WO2000035515A1 - Intravascular cardiac assist device and method

Info

Publication number: WO2000035515A1
Application number: PCT/US1999/029883
Authority: WO
Inventors: Paul Paspa; Rex Nagao
Original assignee: Corvascular, Inc.
Priority date: 1998-12-15
Filing date: 1999-12-09
Publication date: 2000-06-22
Also published as: AU2188700A; WO2000035515A9

Abstract

An intravascular cardiac assist device is disclosed which in one embodiment comprises an elongated tubular member adapted for insertion into a blood vessel, such as a pulmonary artery, the tubular member comprising a lumen defining a perfusion path within the vessel through the tubular member, an inlet port, an outlet port, an optional inlet valve associated with the inlet port and an optional outlet valve associated with the outlet port, and an inflatable member positioned in the lumen and selectively moveable between a deflated position and one or more inflated positions during which blood is propelled from the inlet port axially through the lumen and back into the vessel through the outlet port and the optional outlet valve.

Description

INTRAVASCULAR CARDIAC ASSIST DEVICE AND METHOD

FIELD OF THE INVENTION The present invention relates to cardiac assist devices and methods and more particularly to a novel intravascular cardiac assist device that is configured to be inserted directly into a target vessel, such as a pulmonary artery, and which uses one or more relatively flexible balloons as the blood propelling member(s).

BACKGROUND OF THE INVENTION Minimally invasive surgical techniques have revolutionized cardiac surgery. Minimally invasive techniques have been developed to attempt to reduce or eliminate some of the more serious complications of conventional open-chest cardiac surgery techniques, such as the morbidity associated with the use of cardiopulmonary bypass. Minimally invasive techniques enjoy the advantages of reduced morbidity, quicker recovery times, and in some cases improved cosmesis over conventional open-chest cardiac surgery in which the surgeon "cracks" open a patient's chest by sawing through the breastbone or sternum. Recent advances in endoscopic instruments and percutaneous access to a patient's thoracic cavity have made minimally invasive surgery possible. Reduction in morbidity, lower cost, and reduced trauma has made minimally invasive surgery desirable. One approach to minimally invasive cardiac surgery is an endoscopic procedure in which access to the heart is gained through several small openings, or ports, in the chest wall of a patient. The endoscopic method allows surgeons to stop the heart without cracking the chest by utilizing a series of internal catheters to stop blood flow through the aorta and to administer a conventional cardioplegia solution (e.g., a potassium chloride solution) to facilitate stopping the heart. The cardioplegia solution paralyzes the electrical activity of the heart and renders the heart substantially motionless during the surgery. The endoscopic approach utilizes groin cannulation to establish cardiopulmonary bypass (CPB) which takes over the function of the heart and lungs by circulating oxygenated blood throughout the body. After CPB is started, an intraaortic balloon catheter that functions as an internal aortic clamp by means of an expandable balloon at its distal end is used to occlude blood flow in the ascending aorta from within. A full description of an example of one preferred endoscopic technique is found in United States Patent No. 5,452,733, the complete disclosure of which is incorporated by reference herein. A primary drawback of endoscopic cardiac surgery procedures, however, is that such procedures do not avoid the damaging effects of CPB. CPB has been shown to be the cause of many of the complications that have been reported in conventional coronary artery bypass graft (CABG) procedures, such as complement and neutrophil activation, adverse neuropsychologic effects, coagulopathy, and even stroke. The period of cardiopulmonary bypass should be minimized, if not avoided altogether, to reduce patient morbidity.

An approach to minimally invasive cardiac surgery that avoids CPB is minimally invasive direct coronary artery bypass grafting (MIDCAB) on a beating heart. Using this method, the heart typically is accessed through a mini-thoracotomy (i.e., a 6 to 8 cm incision in the patient's chest) which also avoids the sternal splitting incision of conventional cardiac surgery. The anastomosis procedure is then performed under direct vision on the beating heart without the use of CPB or potassium chloride cardioplegia. Most investigators in the field at present believe that elimination of CPB is less invasive and preferable to elimination of the median sternotomy. However, there are many obstacles to precise coronary anastomosis during MIDCAB on a beating heart. In particular, the constant translational motion of the heart and bleeding from the opening in the coronary artery hinder precise suture placement in the often tiny coronary vessel.

In response to problems associated with the above-described minimally invasive surgical techniques, a new minimally invasive surgical platform known as the Transarrest™ platform has been developed to minimize the cardiac motion of the beating heart while avoiding the need for CPB and conventional cardioplegia. The Transarrest™ platform employs a novel pharmaceutical approach to stabilizing the heart. This revolutionary pharmaceutical approach to cardiac stabilization is fully described in co-pending nonprovisional patent application for Compositions, Apparatus and Methods For Facilitating Surgical Procedures, Serial No. 09/131,075, filed August 7, 1998 and invented by Francis G. Duhaylongsod, M.D, the entire contents of which are expressly incorporated by reference herein. As described therein, pharmaceutical compositions, devices, and methods are provided which are useful for medical and surgical procedures which require precise control of cardiac contraction, such as minimally invasive CABG procedures. Generally, the Transarrest™ platform involves the administration of a novel cardioplegia solution which provides for precise heart rate and rhythm control management while maintaining the ability of the heart to be electrically paced (i.e., which does not paralyze the electrical activity of the heart as with conventional cardioplegia solutions). Specifically, the novel cardioplegia solution comprises a pharmaceutical composition which is capable of inducing reversible ventricular asystole in the heart of a patient, while maintaining the ability of the heart to be electrically paced. "Reversible ventricular asystole" refers to a state wherein autonomous electrical conduction and escape rhythms in the ventricle are suppressed. A state of the heart may be induced wherein the heart is temporarily slowed to at least about 25 beats per minute or less, and often about 12 beats per minute or less. The induced ventricular asystole is reversible and after reversal, the heart functions are restored, and the heart is capable of continuing autonomous function. The pharmaceutical composition may preferably include, for example, an atrioventricular ("AV") node blocker and a beta blocker. As used herein, the term "AV node blocker" refers to a compound capable of reversibly suppressing autonomous electrical conduction at the AV node, while still allowing the heart to be electrically paced to maintain cardiac output. Preferably, the AV node blocker, or the composition comprising the AV node blocker, reduces or blocks ventricular escape beats and cardiac impulse transmission at the AV node of the heart, while the effect on depolarization of the pacemaker cells of the heart is minimal or nonexistent. The beta blocker is provided in one embodiment in an amount sufficient to substantially reduce the amount of AV node blocker required to induce ventricular asystole. For example, the AV node blocker may be present in the composition in an amount which is 50% or less by weight, or optionally about 1 to

20% by weight of the amount of AV node blocker alone required to induce ventricular asystole.

In one embodiment to induce reversible ventricular asystole in a patient, the beta- blocker propranolol and the AV node blocker carbachol are serially administered in an initial intracoronary bolus to induce reversible ventricular asystole of the heart, and then carbachol is administered as a periodic (e.g., one or more bolus infusions) or a continuous intracoronary infusion to maintain ventricular asystole during the course of the surgical procedure. Electrical pacing wires are connected to the right ventricle and/or left ventricle and/or atria and are used to pace the heart using a novel foot-actuated pacer control system to maintain the patient's blood circulation during the periods in which the surgeon is temporarily not performing the surgical procedure. Thus, for example, in a CABG procedure, the surgeon can control the pacing of the heart with a convenient foot pedal and can controllably stop the heart as sutures are placed in the vessel walls. The pharmaceutical compositions, devices and methods for drug delivery, and systems for pacing the heart, give a surgeon complete control of the beating heart. The Transarrest™ procedure described above can be used to facilitate any surgical procedure within the thoracic cavity or other body cavity which requires intermittent stoppage of the heart or elimination of movements caused by pulsatile blood flow, whether access is gained to the body cavity via a partial or median sternotomy incision, via a mini-thoracotomy incision, or via one or more small incisions or ports in the chest wall.

At the present time, however, the avoidance of CPB in MIDCAB cardiac procedures such as the Transarrest™ procedure described above (in which the heart itself is used to maintain systemic blood circulation) essentially limits the procedure to single and double-vessel CABG procedures on the anterior surface of the heart. Complex multiple- vessel procedures often require lifting and manipulating the heart to access the posterior surface of the heart. Even moderate turning of the heart while it is beating (or temporarily stilled by an intermittent pacing interruption) can cause valvular regurgitation and aortic crimping, (and potential crimping of other vessels which supply blood to or receive blood from the heart, such as the pulmonary artery), which can disrupt the patient's blood flow, especially to the right side of the heart which pumps blood to the pulmonary artery at significantly lower pressures than the left side of the heart. Due to this hemodynamic compromise in right ventricular function, it is currently difficult to access obstructions located in vessels on the side, bottom or back of the heart (such as the distal portions of the right coronary artery (e.g., the posterior descending right coronary artery) and the circumflex vessels) using the Transarrest™ procedure or any other beating heart approach.

Several devices have been developed to attempt to improve a surgeon's ability to manipulate the heart. A variety of intravascular in-line axial flow-assist devices using relatively complex impeller technology have been examined in the experimental laboratory for left heart assist. An example of an axial flow-assist device is the Hemopump® axial flow device manufactured by Medtronic, Inc. (Minneapolis, Minnesota). The percutaneous Hemopump is a 14-25 Fr catheter device that can be placed in the femoral artery and, by radiographic or sonographic guidance, passed across the aortic valve and into the left (or right) ventricle. The device can also be extended partially into the pulmonary artery from the right ventricle to be used for right heart assist. This percutaneous device consists of an outflow cannula, a tiny impeller, and a pump driving system. The Hemopump impeller- based system is capable of adding 2.5 liters/min of support to the left and/or right ventricle. Although this device may be effective in providing right heart assist, its use of an impeller as the blood propelling mechanism can easily lead to hemolysis, e.g., damage to blood cells and other blood constituents which can lead to increased thromboembolism. Also, the Hemopump and other similar impeller-driven pump devices are relatively complex systems which are typically designed for the higher pressures required for left heart assist. These impeller driven devices are also not designed to mimic the natural pulsatile nature of the heart, which may be desirable in certain situations, especially in a beating heart surgical procedure where the heart is pulsating. Other proposed methods of circulatory support include extravascular devices such as a "short-circuit" left ventricular assist device described in U.S. Patent No. 5,599,173 to Chen et al. This device allows access to the posterior circulation through a sternotomy, but without CPB. The short-circuit centrifugal flow-assist device is placed from the right superior pulmonary vein to the aorta for the time required to perform an anastomosis of the posterior and lateral portions of the left ventricle, thus allowing access to all coronary circulation without CPB. There are also numerous examples of other extravascular pulsatile, circulatory heart assist pumps which are either pneumatically operated (having blood and gas containing compartments separated either by a diaphragm or a blood-filled bladder) or which utilize an inflatable balloon as the blood propelling member. These extravascular devices are configured for connection either in parallel with or to one side of the heart external to any blood vessel for temporary mechanical support. Examples of such devices include those disclosed in U.S. Patent Nos. 3,550,162, 4,015,590, 4,116,589, and 4,245,622.

The present cardiac assist device is an intravascular device of relatively simple construction that uses an inflatable balloon as the blood propelling member and that is configured to be inserted directly into a vessel such as the pulmonary artery and to be used for heart surgery, post operative support and other uses. The device is configured to provide the requisite support to the heart to allow it to be lifted and manipulated during surgical procedures in which the heart itself is used to maintain systemic blood circulation without the associated high cost and complexity of prior devices. SUMMARY OF THE INVENTION The present invention is directed to an intravascular cardiac assist device that in one embodiment includes a flexible tubular member adapted for direct insertion into a vessel, such as the pulmonary artery, for example. The tubular member defines a central lumen therethrough which defines a blood perfusion path through the tubular member and provides a perfusion path through the vessel. A flexible inflatable member such as a balloon is positioned in the lumen and serves as the blood propelling member. The inflatable tubular member preferably has a varying durometer hardness (or varying thickness and flexibility) along its length to allow the inflatable member to inflate more quickly at the inlet end of the device than at the outlet end. Accordingly, as inflation of the inflatable member continues, the inlet end of the device tends to inflate more quickly then the outlet end of the device which helps seal the inlet end of the device to aid in pumping blood within the main lumen towards the outlet end. The flexible tubular member optionally includes an integral inlet valve (such as a flexible flap valve, check valve or other suitable valve) and an integral outlet valve (such as a flexible flap valve, check valve, or other suitable valve) with the inlet valve being in fluid communication with a blood inlet port in the tubular member and the outlet valve being in fluid communication with a blood outlet port in the tubular member. The valves are each operable between open and close positions by alternating positive and negative pressure differentials generated in the tubular member during cyclical actuation (e.g., inflation and deflation) of the inflatable member to provide unidirectional blood flow through the vessel and the tubular member.

In another aspect of the present invention, the outer surface or profile of the tubular member is configured to sealingly engage the inside of the vessel into which it is inserted to help retain and anchor the device within the vessel. The tubular member may include one or more occlusion members extending about the tubular member. More specifically, in one embodiment, the tubular member may include first and second occlusion members spaced apart longitudinally from each other. The occlusion members may be in the form of flanges, inflatable balloons or sealing cuffs of any number of constructions or materials designed to engage and seal against the vessel wall. Alternatively, in another embodiment, the one or more occlusion members can include only a single annular balloon which extends about and along the length of the tubular member from its inlet end to its outlet end. The single balloon can be configured such that separate discrete portions of it inflate to engage and seal against the vessel wall at the inlet and outlet end of the device. The remaining portion of the balloon structure between the inflated sealing portions (at the inlet and outlet ends of the device) serves to add support and structure to the tubular member to help it retain its shape within the vessel and provide adequate blood perfusion through the vessel. In such an embodiment, the tubular member may be made from one or more substantially flexible materials such as reinforced elastomeric materials to allow the device to be easily compressed and shaped (e.g., to allow the device to be folded to a substantially compact configuration for ease of insertion), wherein the device can be made substantially rigid in the vessel by inflation pressure applied along the length of the single occlusion balloon. The tubular member may also be constructed of any suitable biocompatible, relatively flexible material such as polyethylene, polyurethane, silicone or other suitable single or composite material. The tubular member may also be made from more rigid materials, such as plastic materials of relatively high durometer. To facilitate insertion of the tubular member into the vessel, the inlet and outlet ends of the tubular member may be beveled.

According to another aspect of the present invention, the intravascular cardiac assist device can include at least two balloons positioned in the tubular member lumen to improve the pumping efficiency of the device. A first small balloon is positioned proximal the inlet port and can be inflated before the second, main pumping balloon. When inflated, the first balloon expands to fill the same outside diameter as the tubular member lumen to form a seal therewith to provide enhanced unidirectional flow through the device. Inflation and deflation of the balloons can be sequenced by connecting the dual balloons to a programmable pump system which is preferably sequenced to the heart's natural rhythm. Thus, the first balloon can be programmed to inflate ahead of the main pumping balloon at the beginning of the heart's systolic pump phase and similarly to deflate first at the beginning of the heart's diastolic pump phase to provide the desired one-way flow through the device. The second balloon may also be designed to deflate together with and at the same time as the first balloon.

Another aspect of the present invention involves a method of providing cardiac assist during a surgical procedure including the method steps of inserting into a blood vessel a tubular member having a lumen extending between an inlet port with an optional inlet valve and an outlet port with an optional outlet valve and having an inflatable member located in the lumen between the inlet and outlet ports, and selectively actuating the inflatable member to cause it to move between a deflated position in which blood is permitted to enter the inlet port through the inlet valve and one or more inflated positions in which blood is propelled from the inlet port through the tubular member lumen and out through the outlet port valve and outlet port. The method can further include sealingly engaging the tubular member with the inside of the vessel wall by inflating one or more inflatable balloons or sealing cuffs extending about the tubular member. The method can include using a guide catheter, cannula or similar introducer device to facilitate introduction of the cardiac assist device into the vessel.

The invention described below solves the deficiencies of the prior art and offers a number of other features and advantages that will be apparent to one of ordinary skill in the art from the following detailed description, accompanying figures and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partial cross-sectional view of an intravascular cardiac assist device constructed according to the principles of the present invention shown inserted into a blood vessel such as a pulmonary artery.

Figure 1A is a sectional view showing one embodiment of the flap valve mechanism of Figure 1 in greater detail.

Figure IB is a partial cross-sectional view of a slightly modified version of the intravascular cardiac assist device of Figure 1 in which the balloon inflation lumens are offset to one side of the tubular member, e.g., provided in a "toe-heel" configuration.

Figure 2 A is a partial cross-sectional view of the device of Figure 1 shown being inserted into a blood vessel such as a pulmonary artery through a cannula positioned into the vessel. Figure 2B is a partial cross-sectional view of the device of Figure 1 after the device folds open into its natural configuration within the blood vessel in which the device is aligned in registry with the longitudinal aspect of the vessel.

Figure 2C is a partial cross-sectional view of the device of Figure 1 following removal of the cannula and prior to inflation of the occlusion member extending about the tubular member.

Figure 2D is a partial cross-sectional view of the intravascular cardiac assist device of Figure 1 shown inserted into a blood vessel with the external occlusion balloon inflated. Figure 2E is a partial cross-sectional view of the intravascular cardiac assist device of Figure 1 shown inserted into a blood vessel with the inlet valve substantially closed to prevent blood loss out of the device and the pumping balloon partially inflated.

Figure 2F is a partial cross-sectional view of the intravascular cardiac assist device of Figure 1 shown inserted into a blood vessel with the inlet valve closed, the outlet valve substantially open, and the pumping balloon substantially fully inflated.

Figure 2G is a partial cross-sectional view of the intravascular cardiac assist device of Figure 1 shown inserted into a blood vessel with the inlet valve substantially open to allow blood flow into the device, the outlet valve substantially closed, and the pumping balloon substantially deflated to allow the device to fill with blood through the inlet opening and the inlet valve.

Figure 3 is an alternative embodiment of the intravascular cardiac assist device of the present invention with first and second balloons positioned within the tubular member.

Figure 4A is a partial cross-sectional view of the intravascular cardiac assist device of Figure 3 shown inserted into a blood vessel with the occlusion balloon inflated, the inlet valve substantially closed to prevent blood loss out of the device and with the first balloon inflated.

Figure 4B is a partial cross-sectional view of the intravascular cardiac assist device of Figure 3 shown inserted into a blood vessel with the first balloon and the second main pumping balloon each substantially fully inflated.

Figure 4C is a partial cross-sectional view of the intravascular cardiac assist device of Figure 3 shown inserted into a blood vessel with the inlet valve substantially open to allow blood flow into the device, the outlet valve substantially closed, and the first and second balloons substantially deflated to allow the device to fill with blood through the inlet opening and the inlet valve.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail with reference to the accompanying drawings wherein like numerals indicate like elements. Although the invention is not so limited, the detailed description describes the invention in relation to placement of the intravascular cardiac assist device in a blood vessel, such as the pulmonary artery, during performance of a MIDCAB procedure on the heart or great vessels, such as a multi-vessel off-pump CABG procedure with or without using the Transarrest™ system generally described above. The preferred use of the device is for performing right heart circulatory assist during the surgical procedure to minimize or eliminate right ventricular dysfunction and help the heart to maintain systemic blood circulation. However, this example is given by way of illustration only and is in no way meant to be limiting. Those of ordinary skill in the art will recognize that the present invention can be used for any surgical procedure in which it is necessary to provide cardiac assist including heart surgery, post-operative support and other similar uses. Further, in the specific realm of cardiac surgery, the present invention can be used in either closed-chest or open-chest surgical procedures.

Referring to Figures 1 and 2 A-2G, a first preferred embodiment of an intravascular cardiac assist device constructed in accordance with the present invention is shown. The illustrated intravascular cardiac assist device is generally referred to as reference numeral 10. The intravascular cardiac assist device 10 includes an elongated tubular member 12 adapted for direct insertion into a vessel, such as the right pulmonary artery, for example. The tubular member 12 can be constructed of any suitable biocompatible material which provides sufficient flexibility to facilitate insertion of the device into a target vessel.

Moreover, the material should be sufficiently rigid to maintain its shape within the target vessel to allow for adequate blood perfusion through the device 10 and to prevent substantial expansion when the blood propelling member is inflated. Suitable materials include, for example, polyethylene, polyurethane, or silicone. The tubular member 10 may be made of composite or reinforced materials including DACRON, KEVLAR, stainless steel, etc. and including certain self-expanding stent supported materials. The tubular member 12 may also be made from substantially flexible reinforced elastomeric materials to allow the device to be compressed and folded to a compact configuration for ease of insertion as described in greater detail below. The tubular member 12 defines a central lumen 14 therethrough extending between an inlet end 18 and an outlet end 20 of the tubular member 12 which defines a blood perfusion path through the tubular member 12 and provides a perfusion path through the vessel. The inlet and outlet ends 18, 20 of the tubular member 12 may be beveled to facilitate insertion of the device 10 into the intended vessel. A flexible inflatable member 16 such as a balloon is positioned in the lumen 14 and serves as the blood propelling member. Inflatable member, or balloon, 16 will be made of a suitable inflatable, preferably nonthrombogenic material to avoid the danger of blood clotting; polyurethane is an example of such material. The inflatable member 16 preferably is composed of at least two or more portions along the length of the inflatable member 16 which are made of varying durometer materials or have varying thicknesses. For example, the elasticity of a portion of the inflatable member 16 closest to the inlet end 18 of the device 10 is greater than the elasticity of the material of the portion of the inflatable member closest to the outlet end 20 of the device to allow the inflatable member 16 to inflate more quickly at the inlet end 18 of the device than at the outlet end 20. Alternatively, the thickness of the inflatable member 16 can increase along its length from the inlet end 18 of the device towards the outlet end 20.

In either situation, as inflation of the inflatable member 16 continues, the inlet end 18 of the device tends to inflate more quickly then the outlet end 20 of the device which, in addition to pumping the blood, helps to direct the flow of blood within the main lumen 14 towards the outlet end 20. After the inflatable member 16 is fully inflated the operation of valves 22,24 ensures that blood flows through the lumen 14 in a direction from the inlet end 18 toward the outlet end 20. Subsequently, the deflation of the inflatable member 16 creates a vacuum or a negative pressure differential within the lumen 14 which forces the outlet valve 24 to close and draws blood into the lumen 14 through the inlet end 18. The thicker less flexible portions of the inflatable member 16 ensure that the more flexible portions of the inflatable member 16 towards the inlet end 18 deflate first prior to deflation of the inflatable member 16 adjacent the outlet end 20. In this way, the device 10 assures good blood washout and minimum blood stagnation within lumen 14.

The inflatable member 16 has an interior which is in fluid communication with a flexible inflation/deflation lumen 15 coupled to one side of tubular member 12 at a generally central location along the length of the tubular member 12 providing the overall device 10 with a generally T-shaped configuration. To facilitate insertion of the device 10 into the intended vessel, the inflation lumen 15 (as well as adjacent inflation lumen 46 described below) could also be provided in a "toe-heel" configuration in which lumens 15 and 46 are offset from the centerline through the vertical dimension of the tubular member 12 and located proximal the inlet end 18 (Figure IB) or outlet end 20 of the tubular member 12. Inflation/deflation lumen 15 in turn is fluidly coupled to a conventional pulsed source of inflation fluid, or control unit (not shown), which is preferably programmed to inflate and deflate inflatable member 16 in synchronization with the natural rhythm of the heart beat in a manner well known in the art. The flexible tubular member 12 may optionally include an integral inlet valve 22 and an integral outlet valve 24 with the inlet valve 22 being in fluid communication with a blood inlet port 26 at the inlet end 18 of the tubular member and the outlet valve 24 being in fluid communication with a blood outlet port 28 at the outlet end 20 of the tubular member 12. The valves 22 and 24 are each operable between open and close positions by alternating positive and negative pressure differentials generated in the tubular member 12 during cyclical actuation (e.g., inflation and deflation) of the inflatable member 16 to provide unidirectional blood flow through the vessel and the tubular member 12. It is to be appreciated, however, that where the inflatable member 16 is configured to vary in elasticity along its length as described in the preferred embodiment above, the operation of the inflatable member 16 alone may provide the requisite unidirectional fluid flow through the device 10 such that the provision of inlet valve 22 and/or outlet valve 24 may not be required.

When employed, the valves 22 and 24 may be of conventional design and can include a flap valve, check valve, tilting disc-type valve, diaphragm valve, gate valve, ball valve, spool valve, poppet valve, duck-bill valve, or other suitable valve configuration. For example, Figure 1 A shows a detailed sectional view of a preferred flap valve design 31 which may be employed as the inlet valve 22 and the outlet valve 24. Fluid flow through the flap valve structure occurs whenever the pressure on the inlet side (left-hand side of the valve structure shown in the figure) is greater than the pressure on the outlet side (right- hand side of the valve structure shown in the figure) and further wherein the pressure differential is of sufficient magnitude to overcome the restriction caused by the two valve flap portions 30 and 32. The flaps 30 and 32 are preferably formed of a flexible elastic material capable of flexing to permit device insertion into the intended vessel and capable of resuming their normal configuration until the appropriate pressure differential exists across the valve structure whereby the valve flaps are forced apart to permit blood flow from the inlet side to the outlet side of the device 10. When the pressure differential is reversed, flaps 30 and 32 are forced into engagement with one another so as to seal the inlet and/or outlet ends of the device. Other configurations of flap valves, such as a tricuspid design, for example, may be suitably employed in the invention, although not as preferred as a bi-flap design.

The outer surface or profile (or portion thereof) of the tubular member 12 may optionally be configured to seal against the inside of the vessel wall. This may be accomplished by configuring the tubular member 12 to have an outside diameter or profile that is substantially the same as or larger than the inside diameter of the intended vessel. Optionally, as shown in Figure 1, the tubular member 12 may include one or more occlusion members extending about the tubular member 12. More specifically, in the embodiment shown in Figure 1 , the one or more occlusion members can include a single annular occlusion balloon 40 which extends about and along the length of the tubular member from its inlet end 18 to its outlet end 20. Occlusion balloon 40 has an interior which is in fluid communication with a balloon inflation lumen 46. The occlusion balloon 40 can be configured such that only those portions of the balloon near the inlet end 18 and outlet end 20 of the device (indicated by reference numerals 42 and 44, respectively) inflate to engage and seal against the vessel wall. The remaining portion of the balloon structure 45 between the inflated sealing portions 42 and 44 serves to add support and structure to the tubular member 12 to help it retain its shape within the vessel and provide adequate blood perfusion through the vessel. In such an embodiment, the tubular member 12 may be made from one or more substantially flexible materials such as reinforced elastomeric materials to allow the device 10 to be easily compressed and shaped (e.g., to allow the device to be folded to a substantially compact configuration for ease of insertion as shown for example in Figures 2A-2C), wherein the device 10 can be made substantially rigid once inserted in the vessel by inflation pressure applied along the length of the single occlusion balloon 40. In alternative embodiments, the one or more occlusion members can include first and second inflatable low-pressure balloons spaced apart longitudinally from each other and which each have an interior which is in fluid communication with the balloon inflation lumen 46. The occlusion members may also be in the form of flanges or sealing cuffs of any number of constructions or materials designed to engage and seal against the vessel wall. The balloons, sealing cuffs, flanges and the like again help to secure the tubular member 12 in the vessel during use of the device 10 and to seal the vessel to force blood through the device. The use of low-pressure balloons has the advantage of allowing the tubular member 12 to expand to effectively fit the size of the particular vessel into which the device 10 is inserted. The inventive method of providing cardiac assist during a surgical procedure with the device 10 of the present invention is described below with respect to a MIDCAB procedure such as a multi-vessel off-pump CABG procedure using the novel Transarrest™ system. As noted above, this particular method is for illustration purposes only and is in no way intended to limit the invention to its use in a MIDCAB procedure. The present invention can be readily placed in any vessel, especially those that supply blood to or drain blood from the heart (such as the inferior or superior vena cavae), and can be used in any heart surgery procedure, for post-operative cardiac support following a surgical procedure, and for other uses as well. The present invention can also be used in closed-chest or open- chest surgical procedures.

A MIDCAB procedure, like any other cardiac surgery operation, requires adequate access to the heart prior to placement of the cardiac assist device 10. Different methods of access can be used by the surgeon to expose the heart such as an anterior left/right thoracotomy, a partial or median sternotomy, a parasternal thoracotomy, and an upper midline incision. Most preferably, a 6 to 8 cm left thoracotomy incision is used to access the heart. With the heart so exposed, an incision on the order of about 5 to 12 mm is made in the pulmonary artery 50 or other target vessel at the desired cardiac assist site, preferably near the pulmonic valve which separates the pulmonary artery 50 from the right ventricular chamber of the heart. Subsequently, both the inlet end 18 and the outlet end 20 of the tubular member 12 are introduced into the pulmonary artery 50 through the incision. This can be accomplished directly by the surgeon by guiding the device 10 with his or her hands or via forceps or tweezers through the incision. Alternatively, as shown in Figures 2A-2C, the device 10 may be guided into the target vessel through the incision therein with the use of a suitable guide cannula 60, catheter or like device.

Due to the flexible nature of the device 10 including the flexible nature of valves 22 and 24, the device 10 can easily be bent into the folded configuration of Figure 2A and telescopically inserted into and pushed through the guide cannula 60. This can be done by the surgeon prior to the procedure or alternatively the device 10 can be pre-packaged with it inserted into cannula 60. Once the cannula 60 and device 10 as a unit are aligned with the incision site, with the distal end of cannula 60 positioned through the incision, the device 10 can be pushed through the lumen of the cannula 60 by applying a downward pressure on the inflation/deflation lumens 15 and 46 or by grasping inflation/deflation lumens 15 and 46 while sliding the cannula 60 with respect to the lumens back through the incision. As the device 10 moves through the distal end of the cannula 60 and into the intended vessel 50, the device will tend to naturally open to resume its natural configuration in which inlet and outlet ends 18 and 20, respectively, are aligned in registry with the longitudinal aspect of the vessel lumen 50, as shown in Figure 2B. If necessary, saline solution or another infusate can be injected through inflation/deflation lumen 46 (or 15) to help the device 10 resume its natural configuration. Subsequently, the cannula 60 can be removed prior to full expansion of occlusion balloon 40 as shown in Figure 2C.

If required, cardiac stabilization such as described in co-pending patent application Serial No. 09/131 ,075, for Compositions, Apparatus and Methods For Facilitating Surgical

Procedures, filed August 7, 1998 and invented by Francis G. Duhaylongsod, M.D. (generally described above in the Background Section) may be used to facilitate insertion of the device 10 by temporarily slowing or stopping blood flow through the heart and thus preventing or minimizing blood loss through the pulmonary artery 50. For example, a novel cardioplegia solution including an AV node blocker compound and a beta-blocker compound, for example carbachol and propranolol, can be administered by intracoronary injection, for example, at sufficient dosages to induce and maintain reversible ventricular asystole , while maintaining the ability of the heart to be electrically paced. With the heart in controlled reversible ventricular asystole, the device 10 may be inserted into the target vessel through an incision therein without the risk of excessive blood loss. Once the device

10 is positioned in the vessel, one or more purse string sutures may be secured about the device in the pulmonary artery 50 to secure the device in place and to prevent further blood loss. The heart may then be paced with suitable pacing electrodes attached to the heart until the surgeon is ready to perform the surgical procedure. Once the device 10 is located within the pulmonary artery 50, inflation and expansion of occlusion balloon 40 will cause balloon portions 42 and 44 to expand to effectively fit the tubular member 12 to the size of the pulmonary artery 50. This will firmly position the tubular member 12 within the internal walls of the pulmonary artery 50 and seal the vessel to maximize blood perfusion through it as shown in Figure 2D. Figures 2E through 2G illustrate operation of the device 10 through a typical heart pumping cycle.

Preferably, the inflation and deflation of inflatable member, or balloon, 16 is timed to be in synchronization with the heart's natural beat and pumping rhythm. Thus, during the heart's systolic phase, in which the ventricles contract to drive blood through the aorta and pulmonary artery 50, the inlet valve 22 remains substantially open to allow blood flow into the device from the pulmonary artery 50, the outlet valve 24 is substantially closed, and the inflatable member 16 is substantially deflated to allow the device to fill with blood through the inlet opening and the inlet valve 22. (see Figure 2D). As the heart moves towards its diastolic phase in which the atria and ventricles of the heart relax to fill with blood, the reverse fluid pressure differential created within tubular member 12 will cause inlet valve 22 to become substantially closed, and as inflatable member 16 is inflated, blood will be propelled through the tubular member 12 and out through the outlet valve 24 and outlet opening as shown in Figures 2E and 2F. As shown particularly in Figure 2E, the more flexible (or softer) portions of inflatable member 16 towards inlet end 18 tend to inflate more quickly then the thicker (or harder) portions of the inflatable member 16 near outlet end 20 of the device which helps to pump blood within the main lumen 14 towards the outlet end 20. After the inflatable member 16 is fully inflated the operation of valves 22,24 ensures that blood flows through the lumen 14 in a direction from the inlet end 18 toward the outlet end 20. Subsequently, the deflation of the inflatable member 16 creates a vacuum or a negative pressure differential within the lumen 14 which forces the outlet valve 24 to close and draws blood into the lumen 14 through the inlet end 18.

Figures 3 and 4A-C show an alternative embodiment of the present invention (and its operation) in which the intravascular cardiac assist device 10' includes at least two balloons positioned in the tubular member lumen to further improve the pumping efficiency of the device. A first small balloon 70 is positioned proximal the inlet end 18' of the device and can be inflated before the second, main pumping balloon 16'. When inflated, the first balloon 70 expands to fill the inside diameter of the tubular member lumen 12' to form a seal therewith to provide enhanced unidirectional flow through the device 10'. The first balloon 70 can be used in combination with inlet valve 22', or the balloon 70 can be used in lieu of valve 22' and can act as both a pumping member and as an inlet valve. The first balloon 70 can be provided with its own separate and independent inflation and deflation lumen 72 as shown in the figures, or a suitable valve or other directional device can be provided in main inflation/deflation lumen 15' to direct the infusion fluid to pass into the interior of balloon 70 before entering the interior of main pumping member 16'.

Because of the additional pumping action and support of first balloon 70, the second balloon 16' can comprise a relatively simple balloon structure of uniform material construction or, of course, it can be configured to have varying durometer hardness or thickness portions along its length as described in previous embodiments for enhanced pumping efficiency. Inflation and deflation of the balloons 16' and 70 can be sequenced as shown in Figures 4A-4C by connecting the dual balloons to a programmable pump system, such as a conventional pump currently used for conventional intra-aortic balloon pump systems, for example. The pump is preferably sequenced to the heart's natural pumping rhythm. Thus, the first balloon 70 can be programmed to inflate ahead of the main pumping balloon 16' at the beginning of the heart's systolic pump phase and similarly to deflate first at the beginning of the heart's diastolic pump phase to provide the desired oneway flow through the device 10'. Alternatively, the first and second balloons 16' and 70, respectively, may be configured to deflate together and at the same time if desired.

All references cited herein are hereby incorporated by reference. The above is a detailed description of one or more particular embodiments of the invention. It is recognized and understood that departures from the disclosed modifications will occur to a person of ordinary skill in the art. For example, the device can be inserted into other vessels which supply blood to or drain blood from the heart other than the pulmonary artery, such as the superior or inferior vena cava, the pulmonary vein, the right ventricle (or a portion thereof), and the aorta. To ensure that the device works in synchronization with the heart's natural beat, the device 10 can be configured to be coupled to the pacing leads used in the Transarrest™ system generally described above, for example, to sense the ventricular contraction and relaxation (i.e., the systolic and diastolic phases) of the heart. Further, although it is preferable to have the device act in synchronization with the heart's natural beat, the device can also be configured to work out of synchronization with the heart's pumping rhythm if desired (e.g., to pump at a frequency which is two or more times the normal beating frequency of the natural heart). The full scope of the invention is set out in the claims that follow and their equivalents.

Accordingly, the claims and specification should not be construed to unduly narrow the full scope of protection to which the invention is entitled.

Claims

1. An intravascular cardiac assist device comprising an elongated tubular member adapted for insertion into a blood vessel, said tubular member comprising a lumen defining a perfusion path within said vessel through the tubular member, an inlet port, an outlet port, and at least one inflatable member positioned in the lumen and selectively moveable between a deflated position and one or more inflated positions wherein said at least one inflatable member propels blood from said inlet port axially through the lumen and back into the vessel through said outlet port.

2. The device of claim 1 wherein said tubular member includes at least one occlusion member which extends from said tubular member to abut the vessel, thereby sealing at least a portion of said tubular member with the vessel.

3. The device of claim 2, wherein said at least one occlusion member extends about said tubular member from said inlet port to said outlet port.

4. The device of claim 3, wherein said at least one occlusion member includes a balloon which has at least two portions being longitudinally spaced apart which are configured to engage and seal against an inner wall of the vessel when inflated to define an occlusion section which is substantially fluidly sealed from said perfusion path.

5. The device of claim 1 wherein said tubular member includes first and second occlusion members which extend about said tubular member, said first and second occlusion members being longitudinally spaced apart to define an occlusion section which is substantially fluidly sealed from said perfusion path.

6. The device of claim 5 wherein said occlusion members comprise flanges extending from an outer surface of said tubular member, said flanges configured to engage an inner wall of the vessel.

7. The device of claim 5 wherein said occlusion members comprise first and second longitudinally spaced inflatable balloons configured to engage an inner wall of the vessel.

8. The device of claim 1 further comprising an inlet valve associated with said inlet port and an outlet valve associated with said outlet port.

9. The device of claim 8 wherein said inlet valve and said outlet valve comprise one-way valves.

10. The device of claim 9 wherein said inlet valve and said outlet valve comprise flap valves.

11. The device of claim 10 wherein said flap valves are made from an elastomeric material.

12. The device of claim 1 wherein said tubular member is configured to fit within a pulmonary artery of a patient.

13. The device of claim 1 wherein said tubular member is configured to fit within an inferior or a superior vena cava of a patient.

14. The device of claim 1 wherein said at least one inflatable member comprises a balloon.

15. The device of claim 14 wherein said balloon comprises at least two portions along a length of said balloon, each of which are made from a material of a different hardness from the other.

16. The device of claim 14 wherein said balloon comprises at least two portions along a length of said balloon, each of which are made from a material of a different thickness from the other.

17. The device of claim 16 wherein a thickness of said balloon near said inlet port of said tubular member is less than a thickness of said balloon near said outlet port of said tubular member.

18. The device of claim 14 wherein a portion of said balloon proximal said inlet port of said tubular member is more flexible than a portion of said balloon proximal said outlet port of said tubular member.

19. The device of claim 1 wherein said tubular member comprises a plastic material selected from the group consisting of polyurethane, polyethylene and silicone.

20. The device of claim 1 wherein said at least one inflatable member comprises first and second balloons.

21. The device of claim 20 wherein said first balloon is configured to inflate before said second balloon.

22. The device of claim 20 wherein said first and second balloons are configured to be coupled to a programmable pump system which is sequenced to a heart's natural beat.

23. The device of claim 1 wherein said tubular member is made from a flexible reinforced elastomeric material.

24. A method of providing cardiac assist to a patient's heart during a surgical procedure including inserting into a blood vessel having a vessel wall a tubular member having a lumen extending between an inlet port and an outlet port and having at least one inflatable member located in the lumen between the inlet and outlet ports, and selectively actuating the at least one inflatable member to cause it to move between a deflated position in which blood is permitted to enter the inlet port and one or more inflated positions in which said at least one inflatable member propels blood from the inlet port through the tubular member lumen and out through the outlet port.

25. The method according to claim 24 further including sealingly engaging the tubular member with an inside surface of the vessel wall by inflating one or more occluding members extending about the tubular member.

26. The method of claim 24 wherein said selectively actuating at least one inflatable member comprises sequentially actuating a first balloon positioned within the tubular member to inflate and then inflating a second balloon positioned in the tubular member adjacent said first balloon.

27. The method of claim 24 wherein said inserting into a blood vessel comprises inserting the tubular member at least partially into a pulmonary artery.

28. The method claim 24 wherein said inserting into a blood vessel comprises inserting the tubular member at least partially into an inferior or superior vena cava.

29. The method of claim 24 wherein said selectively actuating at least one inflatable member comprises cyclically inflating and deflating at least a first balloon positioned within the tubular member, wherein the balloon includes two or more portions each having a different durometer hardness from at least one other of the portions.

30. The method of claim 24 wherein said selectively actuating at least one inflatable member comprises cyclically inflating and deflating at least a first balloon positioned within the tubular member wherein the balloon includes two or more portions each have a different wall thickness from at least one other of the portions.

31. The method of claim 24 wherein said selectively actuating an inflatable member comprises cyclically inflating and deflating the inflatable member in synchronization with the heart's own natural beat.

32. A method of providing cardiac assist to a heart of a patient during a surgical procedure in which the heart is used to maintain systemic blood circulation during the procedure comprising inserting at least one inflatable member into a blood vessel through an incision therein and inflating and deflating the inflatable member at least once during the surgical procedure to assist the heart in pumping blood through the blood vessel.

33. The method of claim 32 wherein said inflating and deflating the inflatable member comprises inflating and deflating the inflatable member in synchronization with the heart's own natural beat.

34. The method of claim 32 wherein inserting at least one inflatable member into a blood vessel comprises inserting the inflatable member into a pulmonary artery of the patient through an incision therein.

35. The method of claim 32 wherein inflating and deflating the inflatable member comprises cyclically inflating and deflating the inflatable member at a frequency which is greater than a frequency of the heart's own natural beat.

36. The method of claim 32 wherein the inflatable member is located within an elongated tubular member which is configured to be inserted into said vessel.