Biomedical Engineering Reference
In-Depth Information
Percutaneous procedures, commonly performed for peripheral and cor-
onary angioplasties for several decades, have also been used in valve
disease management; balloon mitral or aortic valvuloplasties are per-
formed as 'salvage' procedures in non-operable patients with acute heart
failure.
8-10
Several companies are now developing devices that could allow
percutaneous treatment of mitral (valve repair and annuloplasty), pulmo-
nary, and aortic (bioprosthetic implant) valves, avoiding open-heart
surgery.
11-15
The aortic valve prosthesis is generally delivered percutaneously via a
specifi c catheter-based technique and implanted within the diseased aortic
valve. The procedure is performed under local (or general) anesthesia and
with femoro-femoral cardiac assistance. Seven years after the fi rst case in a
person, transcatheter aortic valve implantation represents a dynamic fi eld
of research and development. At the present time two devices have been
CE-marked for this purpose and are being commercialized, the Edwards
SAPIEN valve (Edwards Lifescience, Irvine, CA) and the CoreValve valve
(Medtronic Inc., Irvine, CA). Technological improvements allowing the use
of smaller arterial sheaths to decrease vascular trauma, ameliorated cath-
eters to facilitate valve delivery, and valves with long-term durability are
the focus for improvement in this fi eld, and these could extend the suitabil-
ity of this technology to a wider cohort of patients. The authors of this
chapter have extensive experience with the CoreValve technology, and this
device will be the focus of most of the material discussed with this work.
However, where appropriate, reference will be made to alternative tech-
nologies, including the Edwards SAPIEN device.
5.2
Material
In general terms, percutaneous valve implantation is the delivery of a fold-
able heart valve that can be mounted on an expandable or self-expandable
stent. The CoreValve aortic valve prosthesis (AVP) consists of a self-
expanding nitinol heart valve cage designed for the replacement of a native
valve or an in-place bioprosthetic aortic heart valve. The Edwards SAPIEN
valve consists of pericardial leafl ets fi xed to a balloon-expandable steel
stent. These chemically fi xed xenograft valves, however, also share some
problems with their surgical valve analogs. Problems include immunogenic-
ity, uncertain durability, rapid calcifi cation in young patients and a relatively
high infection risk. Once deployed, the prosthesis is not retrievable from
the site of expansion. The procedure is performed under local or general
anesthesia. Vascular access is via surgical cut-down for the Edwards
SAPIEN valve and is percutaneous for the CoreValve system with angiog-
raphy and potentially transesophageal echocardiography used to guide
proper positioning of the heart valve.
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