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Aortic valve replacement (AVR) using open heart surgery is a standardized cardiosurgical procedure with the disadvantage of 3 to 4 hours of cardiopulmonary bypass to resect the mostly calcified valve and to sew in the frame of the biological prosthesis.
The aim of the following device is to shorten this time by 75 %, using foldable Nitinol blades to create a circular annulus which allows the use of a self-fixating prosthesis. After further development, the device shall serve for minimally invasive surgery as part of transapical off-pump valve replacement through a trocar.
Methods:
Laser-cut T-structures of Nitinol sheet-material have been grinded to produce cutting edges which have been given the shape of half-circles afterwards. These have been connected to each other and to columns by using rivets which serve as articulating axes for the cutting ring.
To insert the cutting edges into the heart through the calcified leaflets, the blades are folded around theses axes and torn into a tube. Once released on the other side of the valve, they regain their shape due to the superelasticity of the material.
By combining rotation of the ring with a translating movement against a fix circular ring of hardly greater diameter on the instrument, a punching process is created which cuts the calcified valve leaflets and leaves a circular annulus.
Specially designed test-specimens have been created to simulate calcified valves. By using them, grinding and cutting parameters, as well as blade-shapes have been tested and optimized.
Conclusions:
Preliminary tests have shown that contraction and expansion of the Nitinol-cutting-rings are possible with acceptable shape stability. The results of the cutting-tests have shown sufficient stiffness and sharpness of the blades to obtain acceptable cutting results by using the rotating punching process. Resection time was very low with around 30 seconds per test-specimen.