RELATED APPLICATION

The present application claims the benefit of U.S. Provisional Application No. 62/458,329 filed February 13, 2017, which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

Embodiments relate to implantable conduits capable of producing or replacing an artery, vein, or other part of a cardiovascular system.

BACKGROUND

Congenital heart defects affect about 1 in 100 live births. Congenital heart defects are the most frequent cause of birth-defect-related deaths worldwide.

Some congenital defects require surgery to rectify defects in the heart. Pediatric cardiac surgery has improved outcomes for children, and children with congenital heart defects are more likely to survive to adulthood than ever before. Nonetheless, conventional procedures for addressing some congenital heart defects can be costly, dangerous to the patient, and improve the patient's cardiac health only temporarily.

One particular type of congenital heart defect is a defective or absent connection between the pulmonary artery and the right ventricle of the heart. The pulmonary artery carries blood from the right ventricle of the heart to the lungs for oxygenation. One-way flow of the blood from the right ventricle to the lungs is created by the pulmonary valve, which in a healthy heart includes three cusps that close to prevent flow of the blood back into the right ventricle.

The pulmonary outflow can be defective in a number of ways. First, the cusps of the pulmonary valve may be ineffective at preventing backwards flow of blood. Alternatively, the pulmonary artery itself may be defective in some way, or in some cases the heart may develop without a pulmonary artery whatsoever, often accompanied by a ventricular septal defect.

Depending on the particular defect, there are a number of surgical procedures used to correct congenital heart defects, the most common of which include Pulmonary Valve Insertion (PVI) and Pulmonary Conduit (PC) replacement. PVI and PC can be used to correct pulmonary stenosis, pulmonary atresia, pulmonary valve absence or leakage, Tetralogy of Fallot, right ventricles having double outlets, transposition complexes, truncus arteriosis, and Ross procedure for aortic valve disease, among others.

Rectifying a congenital heart defect often requires multiple surgeries as the patient grows. Particularly for PVI or PC, where a new conduit or portion thereof is inserted at the patient's heart, the procedure can be required multiple times as the replacement valve and/or conduit do not grow with the rest of the patient's heart.

In addition to size mismatch, the materials used in valve or conduit replacement can present additional difficulties. Homografts (use of human donor artery material) are not available in sufficient quantity to treat the large number of patients with such defects. Furthermore, deterioration and calcification of the graft can cause a need for reoperations.

Porcine or bovine jugular conduit is used in some procedures, but they suffer from deterioration when implanted in children. As such, the valve must be replaced occasionally because the valve will calcify and stop functioning, or because the conduit itself cannot grow with the opening in the heart, or because the artery itself has become rigid and inflexible and is no longer safe.

Reoperation rates for PVI or PC treatments are high. Studies of PVI and PC patients show that 87% of infants undergoing conduit replacement require reoperation within 5 years. Breymann et al., The Contegra Bovine Valved Jugular Vein Conduit for Pediatric RVOT Reconstruction: 4 years experience with 108 patients, J. Cardiac Surgery 426 (Sep. -Oct. 2004). Furthermore, researchers have found an 83% stenosis rate for small-sized conduits of about 12 mm. Aristotle Protopapas and Thanos Anthanasiou, Contegra Conduit for Reconstruction of the Right Ventricular Outflow Tract: a Review of Published Early and Mid-Time Results, 3 J. Cardiothoracic Surgery 62 (2008).

Similarly, bioprosthetic bovine or porcine valves are susceptible to calcification and degeneration. Porcine valves are often not available in sizes appropriate for children and have no growth potential. Bioprosthetic valved conduits are often difficult to handle in infants, are less desirable than homografts, and also lack growth potential.

An alternative to existing conduit replacement technologies is needed that reduces the number of necessary reoperations, and increasing risk of morbidity and mortality with each subsequent reoperation.

SUMMARY

Conduits having an anisotropic capacity for stretching are described herein. Such conduits can be deployed in vascular systems to provide a pathway of care, as they can be expanded circumferentially to provide a cross-section for blood flow that is appropriate for the size of the patient.

The above summary is not intended to describe each illustrated embodiment or every implementation of the subject matter hereof. The figures and the detailed description that follow more particularly exemplify various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying figures, in which:

FIG. 1 is a perspective view of a conduit according to an embodiment.

FIGS. 2A-2C are perspective views of a method for forming a conduit according to an embodiment.

FIGS. 3 and 4 are simplified views of a heart in which an conduit embodiment is used to replace a portion of a pulmonary artery.

FIG. 5 depicts balloon expansion of a conduit according to an embodiment.

FIG. 6 is a flowchart of a method for making a conduit according to an embodiment.

FIG. 7 is a flowchart of a method for resizing a conduit according to an embodiment.

FIGS. 8A-8C depict conduits according to three different recircularization embodiments.

FIG. 9 depicts a valve in a conduit, according to an embodiment.

FIG. 10A is an angiogram of a control, conventional interposition graft placed in the main pulmonary artery. FIG. 10B is an angiogram of an interposition graft placed in a growing main pulmonary artery showing spontaneous expansion.

FIG. IOC is an angiogram of an interposition graft after balloon expansion.

FIG. 10D is an angiogram depicting anastomosis to the right ventricle exhibiting spontaneous expansion of the conduit.

FIG. 11 A is a diagram depicting a conventional, stepwise increase in conduit width.

FIG. 11B is a diagram depicting spontaneous expansion of a conduit along a pathway according to an embodiment.

While various embodiments are amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the claimed inventions to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject matter as defined by the claims.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments described herein include conduits that can be used to replace or create portions of vascular systems. In particular, disclosed embodiments may be useful to treat defects in children, because the conduits can be circumferentially expanded as desired, such as when a patient grows. The conduits and methods for their uses described herein can be particularly useful in treating congenital heart defects that affect children, by reducing the frequency and total number of surgical interventions necessary. For example, the conduits and methods described herein can be used for right ventricle to pulmonary artery conduit insertion, right ventricle to pulmonary artery conduit change, pulmonary artery reconstructions, and extracardiac conduit Fontan operation, among others.

FIG. 1 is a perspective view of a conduit 100 according to an embodiment. Conduit 100 includes an annular wall 102 and a seam 104.

Conduit 100 is a device or part of a system that can be used to couple together portions of a cardiovascular system. Conduit 100 can be made from a material that is stretchable and/or expansible circumferentially. In embodiments, conduit 100 should be biocompatible, such that it can be placed within the vasculature of a patient. In addition to biocompatibility, it may be beneficial for conduit 100 to resist bacterial buildup, and to be non-clotting. In embodiments, conduit 100 is also flexible, such that it can conform to the size and shape of adjacent portions of the patient's body even during movement of the patient. Further, conduit 100 should resist calcification and hardening, in embodiments.

Annular wall 102 forms the outer wall of a plenum when attached to the vasculature of a patient. For example, annular wall can form a plenum such as a replacement portion of an artery. In embodiments, annular wall 102 is formed of a stretchable polymer such as polytetrafluoroethylene (PTFE). In one embodiment, annular wall 102 is formed of a foamed PTFE layer that is thick enough to prevent leakage of blood or plasma. For example, in one embodiment, annular wall 102 comprises a layer of PTFE having a thickness of at least 1 mm, or alternatively having a thickness of at least 1.25 mm. In embodiments, the thickness of annular wall 102 is selected in combination with the material such that annular wall 102 is thick enough to be impermeable to fluids traveling therein, and yet also thin enough to be conformable for attachment to the vascular system of a patient.

Seam 104 is a result of recircularizing an anisotropic PTFE tube to be circumferentially expandable, as described in more detail with respect to FIGS. 2A-2C. In embodiments, seam 104 can be surgical stitches. In alternative embodiments, seam 104 can be a weld line formed by a thermal or sonic welder, for example.

Conduit 100 as shown in FIG. 1 is shaped substantially as an open-ended cylinder. In alternative embodiments, conduit 100 could take a different shape in order to better conform with various parts of the vascular system in which it will be used. For example, in embodiments where conduit 100 is configured for attachment to a human heart, an end of annular wall 102 can have an angled, curved, or beveled edge, rather than forming a right cylinder as shown in FIG. 1.

In embodiments, conduit 100 is anisotropic, in that it stretches more circumferentially than longitudinally. Furthermore, in embodiments conduit 100 has some hysteresis or malleability. Therefore conduit 100 can be expanded circumferentially, and will remain expanded at least some portion of the amount it was stretched. In embodiments, malleability of conduit 100 permits for circumferential growth by, for example, expanding a balloon inside conduit 100. Additionally or alternatively, conduit 100 can expand over time as a result of pressure within the plenum formed by annular wall 102.

For example, conduit 100 may be positioned between the right ventricle and a pulmonary artery, in embodiments. Depending on the age and size of the patient, an appropriately sized conduit connecting the right ventricle and the pulmonary artery can be anywhere from less than 10 mm for an infant to 2 cm or more for an adult. When a conduit (e.g., conduit 100) is located in this position for a young patient, the conduit may need to be able to expand in order to provide sufficient cross- sectional area for blood flow. Conduit 100 can be expanded manually (as described in more detail with respect to FIG. 5), as needed, and/or conduit 100 can circumferentially distend without any outside intervention. Conduit 100 thereby provides a replacement for defective or missing components of the vasculature of a growing child without requiring reoperation as frequently, because conduit 100 is capable of expanding to match a desired size for the growing child.

Another example is use in extracardiac conduit Fontan (ECC). The ECC Fontan is usually delayed until the child is at least four or five years of age, or at least 15 kg, so that an adult sized conduit (about 20 mm) can be inserted. According to embodiments, the ECC Fontan can be performed as 2 or 3 years of age, with a 14mm conduit that can be expanded to 20-22 mm over time with patient growth, for example. Hence, an earlier Fondan can be done, allowing the child to avoid the prolonged effects of cyanosis.

One material that can be used to provide this growth potential is stretched PTFE. Due to the process by which it is made, stretched PTFE is anisotropic in that it is stretchable a significant amount in one direction, but far less in the perpendicular direction.

FIGS. 2A-2C depict steps in a recircularization process that results in a conduit 200 having anisotropy A such that conduit 200 stretches circumferentially to a greater extent than it stretches longitudinally.

As shown in FIG. 2A, a stretch PTFE tube has anisotropy A. For purposes of FIGS. 2A and 2B, the arrows of anisotropy A indicate the direction in which conduit 200 is more stretchable. Conduit 200 can be a commercially-available piece of stretch PTFE tubing. Commercially-available stretch PTFE tubing, such as GORE-TEX® Stretch Vascular Grafts, have anisotropy as shown in FIG. 2A, and will stretch longitudinally far more than they stretch radially/circumferentially.

FIG. 2A further depicts section 206. The dotted lines of section 206 depict areas of conduit 200 of FIG. 2A that may be cut to result in section 206 of FIG. 2B. As shown in FIG. 2B, section 206 is cut and then rolled, or re-circularized, such that the direction of anisotropy A is circumferential rather than longitudinal. The edges of section 206 can be stitched or otherwise connected to one another to form a right cylindrical conduit, as shown in FIG. 2C.

In alternative embodiments, section 206 can be isolated from an anisotropic material that is not shaped as a conduit. For example, section 206 can be obtained from a sheet of foamed polymer that has been extruded such that it is relatively more stretchable in a first direction than a second direction (i.e., anisotropic with a stretch direction in the direction of extrusion). Sheets, webs, tubes, and other shapes of source material 200 can be created such that a portion that is isolated therefrom has anisotropy A. In those embodiments, an anisotropic conduit that preferentially stretches in the radial direction can be made by circularizing the source material. The source material is not recircularized, in that the source material did not have an annular cross-section at the time it was made.

According to an embodiment, a non-tubular source material can be formed into a conduit by isolating a section of that source material (which could be a sheet, web, or other non-tubular source material). The source material can have a primary stretch direction. The isolated section of anisotropic material can be circularized. Circularization includes forming the source material into a conduit having an annular cross-section. The circularized material forms a conduit, and the primary stretch direction of the source material can be arranged along a circumferential direction of the conduit. As such, the conduit is more stretchable in the radial direction than in the longitudinal direction. The resulting circularized conduit can be coupled to other structures to form a fluidic coupling therebetween. For example, the circularized conduit could be coupled as an interposition graft or anastomosis.

In still further embodiments, a tube may be created that exhibits higher stretchability in the radial direction without recircularization. The radial stretchability of the tube could result from alignment of polymer in the circumferential direction of the tube during or after manufacturing, or due to a post-extrusion conditioning step. Such tubes are circularized, in that they have annular cross-sections and can be used as a conduit as described in more detail below, and may not even require stitching, welding, or other modification to form the desired conduit shape, size, and stretch anisotropy.

FIG. 2C depicts recircularized conduit 206R made from the section 206 described previously with respect to FIGS. 2A and 2B. Recircularized conduit 206R includes stitches 206S, connecting the edges of section 206 as shown in FIG. 2B. Furthermore, anisotropy A is circumferential; that is, recircularized conduit 206R will expand more readily circumferentially than it will expand longitudinally. In embodiments, recircularized conduit 206R can expand by up to 10%, or up to 20% circumferentially, depending on the thickness of the material that makes up section 206. In contrast, recircularized conduit 206R may only expand by up to 1% or up to 2% longitudinally, depending on the thickness of the material that makes up section 206. In addition to stretching elastically more in the direction of anisotropy A, recircularized conduit 206R can deform plastically in the direction of anisotropy A. The extent of plastic deformation in the direction of anisotropy A is greater than the extent of plastic deformation in any other direction, in embodiments. Section 206 of FIG. 2A can be cut such that anisotropy A is maximized in the circumferential direction, and minimized or eliminated entirely in the longitudinal direction, of recircularized conduit 206R.

As will be understood from the foregoing description of FIGS. 2A-2C, the initial circumference of the recircularized section 206R is dependent upon the width of section 206 that is cut from conduit 200 of FIG. 2A. Likewise, the initial length of recircularized section 206R is dependent upon the circumference of conduit 200 of FIG. 2A. In embodiments, a second cut can be made to remove unwanted or undesirable length of recircularized section 206R.

FIG. 3 is a simplified schematic view of a human heart 300. In one embodiment, a conduit (e.g., recircularized conduit of FIG. 2C) can be used to replace a damaged portion of the vasculature shown in FIG. 3, or to create a conduit that is absent due to, for example, a congenital heart defect. FIG. 3 particularly points out two portions of the vasculature: a right ventricle 308, and a pulmonary artery 310. In a healthy heart, right ventricle 308 is a source of blood to pulmonary artery 310. In some heart defects, the connecting structure 312 is absent or damaged, while in others the pulmonary valve (not shown) fails to prevent flow of blood from pulmonary artery 312 back into right ventricle 310.

FIG. 4 shows one particular implementation of a conduit as described herein. As shown in FIG. 4, conduit 400 having seam 402 caused by recircularization is positioned between the right ventricle and the pulmonary artery.

FIG. 5 depicts a system 500 for circumferentially expanding an annular wall 502 that has been recircularized, such that it includes seam 504 and anisotropy A. In the embodiment shown in FIG. 5, a catheter 514 inflates a balloon 516 within annular wall 502 in order to circumferentially expand annular wall 502, as indicated by arrows.

One benefit of system 500 shown in FIG. 5 is that it can be conducted via angioplasty of the conduit at annular wall 502. This procedure is significantly easier and safer than replacement of the conduit, as would often be required using conventional techniques.

In some embodiments, annular wall 502 can expand without being acted upon by balloon 516. In embodiments, the material that makes up annular wall 502 can be selected such that it undergoes circumferential expansion over time at pressures regularly found in a human's vascular system.

For example, in one embodiment annular wall 502 is used to define a flowpath for blood passing from the right ventricle to the pulmonary artery of a patient. Blood pressures within the right ventricle and pulmonary artery are commonly between about 15 mm Hg and about 30 mm Hg. For some materials, including expanded PTFE, exposure to low pressures such as these over time causes plastic deformation that is similar to the rate of the growth that would be expected of a normal conduit between the right ventricle and pulmonary artery. Therefore, a single replacement conduit (such as annular wall 502) can be coupled to the right ventricle and the pulmonary artery, and that replacement conduit will grow with the patient. This reduces the need for reoperation, which is often required for growing children using conventional replacement conduits.

For most children this slow, plastic deformation of the conduit causes the cross-section of the conduit to approximate or match the size that is appropriate for the child's age and size. In the event that the conduit does not grow quickly enough (for example, where a child grows unusually quickly or where blood pressure is lower than normal) balloon-based systems (e.g., 500) can be used to expedite the circumferential growth of the conduit.

In one embodiment, a conduit comprises an annular wall 502 of anisotropic expanded PTFE, recircularized such that it is most stretchable circumferentially and yet exhibits very little stretchability in the longitudinal direction. In its initial, pre-insertion state, the conduit has a diameter of 10-11 mm and a length of 2 cm. Balloon inflation with a 20 mm balloon of the conduit causes increase in the diameter of the conduit as shown in Table 1, below.

Test data show, however, that for many children the use of balloon inflation is not necessary. In initial testing, control grafts measuring 10 mm in diameter were exposed to normal right heart pressures of 15 to 30 mmHg, as were anisotropic conduits. Each month, transthoracic echocardiogram was used to measure conduit dimensions. The results of these tests are shown in Table 2, below.

As shown in Table 2, standard conduits do not increase in size under normal usage. The increase in size of the anisotropic test group, meanwhile, was spontaneous (i.e., without the use of balloon stretching or other intervention by a healthcare professional) and corresponded to the needed expansion rate for a growing child. In embodiments, a varying thickness or more stretchable material could be used to increase the rate of circumferential growth of the conduit, or vice versa, in order to tune a pathway to a patient's expected growth rate.

Accordingly, annular wall 502 provides a new option that has growth potential, with radial expansion properties for use in pediatric cardiovascular surgery that has immediate and direct clinical and translational impact on patient care. Annular wall 502 is a unique cardiovascular conduit with an anisotropic capacity for stretching. Such conduits can be deployed in vascular systems to provide a pathway of care, as they can be expanded circumferentially to provide a cross-section for blood flow that is appropriate for the size and growth needs of the patient. Such conduits are biocompatible, easily available off-the-shelf, and resist calcification and degeneration.

Depending on the age and size of the patient, an appropriately sized conduit connecting the right ventricle to the pulmonary artery can have an unstretched, initial size of 10-12 mm for an infant which can radially expand to 21 mm diameter, which corresponds to an adult size. The conduit thereby provides a replacement for defective or missing components of the vasculature of a growing child without requiring reoperation as frequently, because the conduit is capable of expanding to match a desired size for the growing child into adulthood. The conduit shows spontaneous expansion in vivo and can be balloon-dilated under low pressure as desired.

As shown in FIG. 5, the interior of annular wall 502 is substantially cylindrical and can be smooth and structurally sound, such that annular wall 502 is stentable. Stentability is beneficial because a stent can be used to implant or adjust valves, for example.

FIG. 6 is a flowchart of a method 600 for creating a recircularized conduit (such as recircularized conduit 206R of FIG. 2C, conduit 400 of FIG. 4, or annular wall 502 of FIG. 5). According to the method shown in FIG. 6, an anisotropic polymer tube is provided at 618. As previously described with respect to FIGS. 2A-2C, anisotropic polymer tubes such as stretch PTFE tubes are relatively more stretchable longitudinally than circumferentially.

At 620, the anisotropic polymer tube is sectioned as shown in FIG. 2B to form a tube portion. That is, a portion of the anisotropic polymer tube is cut out to form a portion having a desired size. At 622, the portion is recircularized. Recircularization involves closing the portion at its edges such that it has an annular cross-section and can be formed to use a plenum. At the annular cross-sections, the tube is relatively more stretchable circumferentially than it is stretchable longitudinally.

At 624, which is optional, the recircularized tube portion may be dilated, or stretched circumferentially. This can be performed either before or after implanting the recircularized portion in a patient. Furthermore, dilation can be performed using balloon angioplasty, as described with respect to FIG. 5, or it can occur due to pressure within the plenum caused by the patient's blood flow, as described with respect to FIG. 1.

FIG. 7 is a flowchart of a method 700 for expanding a tube (such as recircularized conduit

206R of FIG. 2C, conduit 400 of FIG. 4, annular wall 502 of FIG. 5, or recircularized tube portion at 622 of FIG. 6).

At 724, vasculature is connected to a recircularized tube, as shown in FIG. 4. The connection can be performed by suturing, crimping, or other surgical techniques.

At 726, growth of the patient's vasculature is monitored. For example, where the patient is a child, the vasculature may grow as the patient ages. Due to growth of the vasculature, it is desirable for the tube to grow circumferentially as well in order to provide sufficient cross-sectional area for blood flow. In embodiments, the material and thickness of the tube can be selected such that some circumferential growth will occur over time.

At 728, a determination is made of whether the tube is too small. This determination can be made by a health care professional based on the size of the tube and the size of the vasculature. In the event that the tube is not too small, no action need be taken and the growth of the patient's vasculature can continue to be monitored.

At 730, if the tube has become too small for the patient's vasculature, a balloon can be inserted into the tube. In embodiments, the balloon can be inserted using a catheter.

At 732, the tube can be expanded circumferentially. Expansion of the tube can be performed by inflating the balloon inserted at 730 until it applies pressure on the tube, pushing the walls of the tube radially outward as shown in FIG. 5. Once the tube has been inflated sufficiently to expand the tube a desired amount, the growth of the patient's vasculature can be monitored, and 726-732 of the method 700 can be repeated as necessary to promote proper sizing of the tube with respect to the vasculature.

FIGS. 8A-8C depict three alternative recircularization schemes that can be used in other embodiments. FIG. 8A depicts a conduit 800A made of multiple strips of material having anisotropy A and connected at seams 806S. FIG. 8B depicts a conduit 800B constructed using a single strip of material having anisotropy A and connected to itself at seam 806S'. FIG. 8C depicts a conduit 800C made of a unitary open cylindrical piece of material having anisotropy A. In each embodiment, the conduit (800A, 800B, 800C) is configured for circumferential expansion.

In embodiments, circumferentially expandable conduits can include valves and/or leaflets. For example, in the embodiments described above in which a circumferentially-expandable conduit replaces a portion of the pulmonary artery, a replacement may be desired for the pulmonary valve.

In the embodiment shown in FIG. 9, conduit 900 houses a valve. FIG. 9 depicts leaflets 934 that form a valve within annular wall 902 of conduit 900. Leaflets 934 can be made of, for example, small intestinal submucosa (SIS) that is sutured to the interior of annular wall 902. In alternative embodiments, a valve can be positioned within a stent housed in conduit 900. The stent (not shown) can be removed, replaced, or modified as necessary. For example, the stent could be replaced with a larger version if conduit 900 is expanded via angioplasty as described above.

Cusps or leaflets of valves can be added to other embodiments described herein. For example, a stretch PTFE tube can be recircularized as shown in FIGS. 2A-2C, and SIS or thin- walled PTFE or other polymeric or biologic leaflets can be formed and sutured to the interior wall thereof. The SIS or other thin-walled (0.1mm-0.4mm) PTFE or other polymer can be intussuscepted to variable heights and can be attached to create a bicuspid or tricuspid valve mechanism. In some embodiments, the SIS valve can be sutured to a PTFE tube internally at one or more positions.

FIG. 10A shows a replacement conduit 1000 arranged between a pulmonary artery 1002 and a right ventricle 1004 as an interposition graft in the main pulmonary artery. A catheter 1006 is positioned in the frame with markers 1008 that are spaced apart from one another every 1 cm on catheter 1006. Replacement conduit 1000 is conventional and non-expansible. FIG. 10B shows angiogram of an interposition graft before balloon expansion, and FIG. IOC is an angiogram of an interposition graft after balloon expansion. Balloon expansion can be used in embodiments to expedite the growth of the conduit where spontaneous expansion is not rapid enough to keep up with the growth of the patient, for example, or where the patient's vasculature is larger than the initial size of the conduit.

FIG. IOC shows expansible conduit 1000' arranged between pulmonary artery 1002' and right ventricle 1004' as an interposition graft in the main pulmonary artery. Catheter 1006' is again positioned in the frame to depict scale with markers 1008' that are spaced apart from one another by 1 cm.

Conventional conduit 1000 is significantly narrower than anisotropic conduit 1000', despite exposure to substantially equivalent pressures for similar amounts of time. Due to the anisotropy of conduit 1000', radial expansion does not correspond to longitudinal expansion. Conduit 1000 has become too small for the corresponding pulmonary artery 1002 and right ventricle 1004, whereas conduit 1000' has grown along a pathway corresponding to the growth of pulmonary artery 1002' and right ventricle 1004'.

Overall, while conduit 1000 remained at 10 mm in diameter, conduit 1000' expanded spontaneously from about 11 mm to about 16-17 mm over three months. Upon removal of conduit 1000', the anastomoses were patent at either end with a smooth surface along the inner wall of conduit 1000' therebetween, with no sign of pseudo-aneurysm or rupture.

FIG. 10D is an angiogram depicting anastomosis to the right ventricle, which has expanded from about 10 mm to about 16 mm spontaneously. In other words, rather than using the conduit as an interposition graft, conduit 1000' can be sewn or otherwise attached to the heart muscle directly.

FIG. 11 A is a chart 1100 depicting a pathway 1102 of conduit diameter as a function of age of a patient. Pathway 1102 indicates a range of acceptable conduit diameters of a healthy, growing child. Pathway 1102 can be, for example, approximately 10-11 mm at age zero, and can increase to a maximum of 20-22mm by adulthood.

Bars 1104 indicate the size of a conventional interposition conduit, such as a homograft as described above. Bars 1 104 show the size range of a typical replacement conduit. The conventional replacement conduits are arranged in bands 1106A, 1106B, 1106C, and 1106D. According to conventional mechanisms, each band 1106A-1106D can correspond to a new conduit. That is, at the age between each band 1 106A-1106D, an operation may be required to remove an old conduit and insert a new conduit.

Alternatively, a balloon can be used to expand the conduit to move from one band to another (e.g., from band 1106A to band 1106B). Although this is less hazardous to the health of the growing child than replacing the conduit, it does require undergoing a medical procedure. Furthermore, between balloon expansions, the size of the conduit may be larger or smaller than the ideal size, as shown by bars 1104 extending either above or below the range of pathway 1102.

FIG. 11B shows an expansion pathway 1102 and bars 1104 according to an embodiment. Bars 1104 depict an increase in diameter of the conduit that is smooth with increasing age, such that bars 1104 are all within pathway 1102. This spontaneous, continuous expansion reduces or eliminates the need for reoperation to replace a conduit. Although balloon expansion is not always required, the procedure can be employed as a catch-up tool if the rate of spontaneous expansion falls behind the rate of growth of the child (i.e., where the slope of pathway 1102 exceeds the rate of increase in diameter of bars 1104 as a function of time).

Spontaneous expansion of the type shown in FIG. 11B is a function of the material, thickness, and density of conduits according to embodiments. For example, the anisotropic PTFE material described in more detail above can exhibit expansion circumferentially but not longitudinally when exposed to standard pressure and temperature at a desired portion of the vasculature (such as between the right ventricle and the pulmonary artery).

In one embodiment an anisotropic, recircularized conduit is made of PTFE having a thickness of 1 mm, and a density of 1-2 g/cm ³ , or more preferably about 1.5 g/cm ³ . As the conduit expands, the overall thickness of the conduit can be thinned and density can increase, to the point where further expansion is not possible. In embodiments, this point of maximum expansion corresponds with the diameter expected of an adult.

Yield strength of a material is the level of stress at which a specific amount of plastic deformation is produced in the bulk material. For PTFE and similar materials, the yield strength is several orders of magnitude higher than the pressures found in a human body. For example, the flextural yield strength of PTFE is about 100,000 mm Hg or higher, whereas the blood pressure found at the right ventricle to pulmonary artery conduit is about 15-30 mm Hg. Therefore there should not be deformation of the PTFE at normal blood pressures.

Elastic deformation may occur due to the periodic nature of blood pressure. Elastic deformation refers to stretching at an elevated pressure that is recovered entirely once the pressure falls back to its original level.

Based on tests of the anisotropic materials described above, plastic deformation of the conduit can occur along the pathway 1102 without ever exceeding the yield strength of the bulk polymer. The choice of material, density, and thickness, as well as the recircularization process, facilitates expansion along pathway 1102 (i.e., slow, plastic deformation without exceeding the yield strength of the material).

The embodiments described herein are advantageous in that they create a "pathway" of treatment, wherein the conduit can grow or be expanded via angioplasty to grow with the patient. Furthermore, the conduits described herein do not calcify, are easy to handle, are more readily available than donor material, and are hemostatic. Conduits that are amenable to catheter-based manipulation with reduced risk of rupture reduce the number of relatively riskier and more costly replacement procedures.

Various embodiments of systems, devices, and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the claimed inventions. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, configurations and locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the claimed inventions.

Persons of ordinary skill in the relevant arts will recognize that the subject matter hereof may comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the subject matter hereof may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the various embodiments can comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art. Moreover, elements described with respect to one embodiment can be implemented in other embodiments even when not described in such embodiments unless otherwise noted.

Although a dependent claim may refer in the claims to a specific combination with one or more other claims, other embodiments can also include a combination of the dependent claim with the subject matter of each other dependent claim or a combination of one or more features with other dependent or independent claims. Such combinations are proposed herein unless it is stated that a specific combination is not intended.

Any incorporation by reference of documents above is limited such that no subject matter is incorporated that is contrary to the explicit disclosure herein. Any incorporation by reference of documents above is further limited such that no claims included in the documents are incorporated by reference herein. Any incorporation by reference of documents above is yet further limited such that any definitions provided in the documents are not incorporated by reference herein unless expressly included herein.

For purposes of interpreting the claims, it is expressly intended that the provisions of 35 U.S.C. § 112(f) are not to be invoked unless the specific terms "means for" or "step for" are recited in a claim.