Prosthetic tubular aortic conduit and method for...

Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Arterial prosthesis – Including valve

Reexamination Certificate

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C623S001290, C623S001280, C623S001240

Reexamination Certificate

active

06352554

ABSTRACT:

FIELD OF THE INVENTION
A prosthetic aortic conduit for replacing a root portion of the aorta and a method for manufacturing the same.
BACKGROUND OF THE INVENTION
The normal internal human aortic root conduit is provided with a sinus portion which has three sinuses (bulges) which surround the aortic valve. These sinuses are called sinuses of Valsalva and are arranged so that the cross-section of the sinus portion has a generally trefoil shape. The diameter and orifice area of the root are greater at the level of the sinus, decrease slightly at the base, but significantly decrease (by 20%) at the level of the sinotubular junction (where the sinus portion connects to the ascending portion of the aorta which supports the two iliac arteries).
The sinotubular junction or sinus ridge and the sinuses of Valsalva are known to be crucial for the normal function of the aortic valve. The sinus ridge is important in causing initial fluid flow eddies inside the sinuses of Valsalva (see Bellhouse B J: Velocity and pressure distributions in the aortic valve.
J Fluid Mech
1969; 37(3): 587-600 and Bellhouse B. J.: The fluid mechanics of the aortic valve. In: Ionescu M. L. , Ross D. N., Woller G. H., eds. Biological tissue heart replacement. London: Butterworth-Heinemann, 1972:32-8). During systole, the aortic valve opens and the eddy currents created prevent the leaflets of the aortic valve from impacting on the aortic wall. Then, at the end of systole, the eddy currents inside the sinuses cause the leaflets of the aortic valve to become almost closed. Furthermore, the sinus curvature is very important in sharing stress with the leaflet. It has been demonstrated that during diastole the sinus walls move outwardly (increasing its circumferential curvature by 16%) taking up part of the load placed on the leaflet. Further it is known (see (Thubrikar M. J., Nolan S. P., Aouad J., Deck D.; Stress sharing between the sinus and leaflets of canine aortic valve.
Ann Thorac Surg
1986; 42(4):434-40)) that the longitudinal length of the sinus changes very little or does not change at all during the cardiac cycle. In other words during the functioning of the aortic valve the sinus moves up and down as a whole without changing its length.
The standard surgical approach in patients with ascending aortic aneurysm or dissection involving the aortic root and associated with aortic valve disease is the replacement of the aortic valve and ascending aorta by means of a composite and valved graft onto which are reattached the two coronary arteries as originally described by Bentall and de Bono in their classical paper (Bentall H. H., De Bono A.: A technique for complete replacement of the ascending aorta,
Thorax
1968; 23: 338-9). The “open” (Carrel button) method of coronary reimplantation was later recommended to decrease the tension on the coronary ostia while minimizing the risk of late false aneurysm formation. This “Carrel button” method has already reduced the incidence of pseudoaneurysm formation mainly through the reduction of the tension on the ostial anastomoses (see Svensson L. G.; Crawford E. S.; Hess K. R.; Coselli J. S.; Safi H. J.; Composite valve graft replacement of the proximal aorta: comparison of techniques in 348 patients.
Ann Thorac Surg
1992, 54(3) 427-370). A modification of the standard technique was also introduced by Cabrol et al (Cabrol C, Pavie A, Gandjbakhch I. et al: Complete replacement of the ascending aorta with reimplantation of the coronary arteries. New Surgical approach,
J Thorac Cardiovasc Surg
1981: 81; 309-15) for those cases of difficult presentation (low lying coronary ostia, calcified coronary ostia, tissue fibrosis in redo cases) where the coronary ostia are reattached to the aortic conduit by interposition of a small conduit made in DACRON. DACRON is the Trade Name for a material formed from straight chain polyester; the material may also be known as TERYLENE.
If the aortic valve leaflets are normal, a valve-sparing aortic root remodelling procedure which keeps the natural patient valve on site is a reasonable alternative in certain individuals. David and Feindel (David T. E., Feindel C. M.: An aortic valve-sparing operation for patients with aortic incompetence and aneurysm of the ascending aorta,
J Thorac Cardiovasc Surg
1992; 103(4): 617-21) described a surgical technique where the dilated aortic root is replaced with a tube made of DACRON fibres and the native aortic valve is integrated within the graft. This method is generally known as the “Tirone David Type I aortic valve sparing procedure”. However, the lack of sinuses in a straight tube graft was found to negatively influence proper valve function, with the consequent risk of decreasing valva longevity (Kunzelman K. S., Grande K. J., David T. E., Cochran R. P., Verrier E. D. : Aortic root and valve relationships. Impact on surgical repair
J Thorac Cardiovascular Surg
1995; 109(2): 345-51).
Thus in the Tirone David Type I technique for valve sparing operations, the use of a straight tube without a sinus component raises several problems: opening and closing of the native valve is not optimal. For example, upon valve opening, the leaflets might impact on the graft and be potentially damaged. The absence or delay in eddy current formation might alter valve closure causing some regurgitation. Furthermore, the diastolic stress is borne only by the leaflet and is not shared with the sinuses causing a potential decrease in leaflet longevity.
An optimal design for root replacement should therefore incorporate sinuses and a sinotubular junction and further refinement of the technique consisted of trimming one end of the aortic tube graft to produce three separate extensions designed to replace the three sinuses. The reshaped DACRON tube was then sutured to the aortic valve remnants (see David T. E., Feindel C. M., Bos J.: Repair of the aortic valve in patients with aortic insufficiency and aortic root aneurysm.
J Thorac Cardiovasc Surg
1995; 109(2) :345-51) to obtain a final configuration resembling more closely the native aortic root. A similar technique was also described by Yacoub el al (Saram M. A., Yacoub M.: Remodeling of the aortic valve annulus.
J Thorac Cardiovasc Surg
1993; 105(3): 435-8) several years previously.
In U.S. Pat. No. 5,139,515 it was proposed to provide an aortic graft having a lower portions provided with “bulges” apparently mimicking the sinuses of Valsalva. However no method to produce such a conduit for use in aortic surgery is described in the patent. U.S. Pat. No. 5,139,515 described a conduit having an “annular wall of a crimped material similar to that of conventional prosthesis”. No indication is actually given of how to obtain the “annularly-spaced radially outward bulges” mimicking the sinuses. Moreover the drawings clearly show that the conduit, including the sinus portion, is provided along its whole length with corrugations which lie perpendicularly to the longitudinal axis of the prosethesis, and which impart longitudinal elasticity to the whole of the conduit. Upon implantation, the graft cannot expand radially outwardly, but has the potential to move and extend in the longitudinal direction of the longitudinal axis of the prosthesis.
Therefore there is still a need for an effective prosthetic conduit to replace the aortic root while providing all the advantages of the natural sinuses of Valsalva.
SUMMARY OF THE INVENTION
It is therefore one of the objects of the invention to provide a prosthetic aortic conduit which overcomes the drawbacks mentioned above and which upon implantation has the ability to expand radially outwardly whilst maintaining a degree of flexibility in the longitudinal direction.
It is another object of the invention to provide a conduit which is specifically designed to closely mimic the sinuses of Valsalva.
A first object of the invention is a prosthetic aortic conduit for replacing a root portion of an aorta which comprises a first tubular portion and a second tubular portion connected together along a substantially common axis. The second

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