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PROJECT 2

ENDOVASCULAR "NET" PROSTHESIS FOR PREVENTION OF ANEURYSM FORMATION IN MARFAN AND OTHER GENETIC DISORDERS OR FOR VERY EARLY STABILIZATION OF OTHER ANEURYSMS

THE HOUSTON AORTIC SYMPOSIUM 2013

Frontiers in Cardiovascular Diseases - The sixth in the series

IN HONOR OF DR FRANK J VEITH

Presentation Video (Houston, Westin Oaks, March 23, 2013)

(4:20 min - double click on video for full screen HD)

- Abstract 585

Endovascular net prosthesis for prevention of aneurysm formation in Marfan and other genetic disorders or for very early stabilization of other aneurysms

Claudio Rossella, MD and Stefano Nazari, MD

Fondazione Alexis Carrel, Italy

The relative slowness of aneurysm formation and progression to rupture indicates that the decrease in the strength of the arterial wall under the aneurysm formation threshold may be very gradual and limited. Consequently one can imagine that measures to increase, even moderately, the mechanical strength of the arterial wall, for example by means of a dacron fabric network, should be successful in preventing aneurysm formations and thus its complications (dissection and rupture), without necessarily requiring complete prosthetic substitution.

The experimental hypothesis is based on the fact that the net prosthesis positioned and maintained in stable contact with the aortic walls (fig 1-A) is spontaneously, gradually covered by the neo-intima (fig 1-B) (as constantly happens with all tube graft currently in use), invaded by fibroblasts and thus stably associated to the aortic wall (fig 1-C).

A significant advantage of this approach is that, if the net mesh is appropriately dimensioned, it may be expected that the blood flow through the collateral branches is not significantly affected (B-arrows), thus allowing application in all aortic tracts overcoming limitations of current endovascular techniques; moreover this may be the only method theoretically able to fully prevent spinal cord ischemic injury.

The structural properties of the aortic wall associated to the intraluminal net prosthesis rely on three factors (fig 2): -1) the structural properties of the net prosthesis, -2) the structural properties of the aortic wall, -3) the strength of the bonds between the aortic wall and the net prosthesis, based substantially on fibroblastic invasion of the net fabric and its permanent integration with aortic wall.

Given the structural adequacy of the net prosthesis (1) (polypropylene thread diameter 0.5mm, mesh 5x5mm) and its mechanical effect of fractioning the aortic wall in the small area of the net mesh (2), crucial to this model is aorta-prosthesis bond (3). In fact if this link is sufficiently strong and stable in the time, it can be hypothesized of being able to stabilize aortic wall and prevent dilatation even independently from the true diameter of the “net” prosthesis, which could not be further distended after that their meshes have been firmly integrated into the aortic wall. The practical consequence is that the precise equivalence between diameter of the net prosthesis and aortic diameter would not be necessary; the prosthesis in fact could be significantly redundant in respect to the effective aortic diameter, thus allowing for its easier adaptability to geometrical irregularity of vascular wall, with- out consequences on its efficiency in keeping stable aortic diameter.

Interestingly enough in this model the endovascular net prosthesis pro- vides aortic wall mechanical support just where the mechanical stress is higher, and thus just where it’s most needed both to prevent further dilatation and to avoid partial (dissection) or total rupture, with the minimal amount of prosthetic material (approximately ≤1/6th of current endoprosthesis volume).

RELATED ILLUSTRATIVE MATERIAL

Note: The meshes of the net used in this model were obviously too small to prevent the eventual occlusion of all collateral brances in the long term; the structural mechanical analysis however showed that meshes 5x5 mm wide, with polipropylen thread .5 mm in diameter, can largely exceed the strenght required by the endovascular pressure in its higher pathologic occurrences while preventing even small collateral branches occlusion. Obviously the ideal dimensioning of the threads and meshes of the net will requires careful evaluations of many factors and may be different in relation with the aortic tract to be strengthened. Below are exemples of possible prototypes

LATEST NET PROSTHESIS PROTOTYPES

Main References

- S NazariF. Luzzana, F. Carli et al (1996)

Aortic wall structural strenghtening by intraluminal net prosthesis to arrest aneurysm prograssion and to prevent dissection and rupture. Experimental assessment of a new therapeutic approach.

Eur J Cardiothor Surg, 1996; 10:264-272 FULL TEXT CLICK HERE

- S. Nazari (2012)

New approaches for treatment and prevention of Aortic Aneurysms

in Front Lines of Thoracic Surgery, Dr Stefano Nazari (Ed), Intech, DOI: 10.5772/25929. free download at http://www.intechopen.com/books/front-lines-of-thoracic-surgery/new-approaches-for- treatment-and-prevention-of-thoracic-aorta-aneurysms

Techno College Award Nominee 2012

EACTS Daily News- Saturday Oct 27, 2012 pag 17 (click to download .pdf file)

last modified April 19, 2013