Percutaneous cardiovascular valve replacement - Biomaterials and Devices for the Circulatory System - page 129

￿ control of the delivery of the prosthesis;

￿ precision of implantation on the aortic valve annulus;

￿ quality of fi xation of the prosthesis to the surrounding tissue;

￿ absence of migration of the prosthesis;

￿ correct perfusion of the coronary arteries.

The sheep model is by far the most common and suitable model for valve
testing due to the fact that the anatomy, above the valve annulus and in
particular the coronary sinus regions, is very close to that of humans. 16-22
The CoreValve frame, with one part located in the vicinity of these sinuses
and bridging the coronary sinuses with an 'ascending aorta segment',
could therefore reproduce the advantage envisioned in humans in this
model. However, the one major difference from human anatomy described
in the literature was confi rmed in these investigations. In the sheep model,
there is no space between the aortic and mitral valve annuli (the so-called
interaortico-mitral ridge) as is well described in humans and noted by
all surgeons performing heart valve replacements. Therefore, since the
CoreValve frame has an element that covers the subannular space and
the inter-aorticomitral ridge, this causes various degrees of mitral
regurgitation.
In these animals arterial access was obtained through the femoral arteries
and the brachiocephalic trunk for the prosthesis implantation. Angiogra-
phies of the ascending aorta and the left ventricle were performed before
implantation for aortic ring measurement, and after implantation for aortic
valve or paravalvular leakage evaluation.

5.5.1 Implantations
In these fi rst generation studies, 35 animals were implanted in total and
modifi cations to the prostheses and delivery catheters were derived from
the results of these investigations.
These studies confi rmed a number of characteristics of the CoreValve
technology, as follows:

￿ ￿ ￿ ￿ ￿

Precise implantation

With the exception of one experiment, the CoreValve heart valve was
delivered with total accuracy. On one occasion, the self-expandable pros-
thesis jumped out of the delivery system. In response to this, a technique
(CoreValve retaining hooks) was subsequently developed and applied to
retain the prosthesis until the external sheath is fully pulled back. This was
an invaluable lesson in relation to the deployment of the technology, and
informed the design of the device for clinical deployment.