Biomedical Engineering Reference
In-Depth Information
5.12 Two examples of specialized holders for mitral valves which minimize
suture looping during implantation. (a) the Cinch
Õ
Implant System, from
TM
Medtronic, Inc.; (b) the Tricentrix
Holder System, from Edwards
Õ
Lifesciences. (Cinch
is a registered trademark of Medtronic, Inc. Reprinted
with permission from Medtronic, Inc. All Rights Reserved. Tricentrix
TM
is a
trademark of Edwards Lifesciences Corporation. Reprinted with permission
from Edwards Lifesciences LLC. All Rights Reserved.)
5.4.6
Service environment of the valve
Finally, it is essential to consider the service environment of the valve and all the
ancillary devices. While many of the standardized tests include test conditions
which attempt to simulate various ranges of the service environment (e.g., low
flow conditions, high pressure conditions), sometimes the specifics of the
service environment are not known or not well defined. Such would be the case
when trying to understand how a new surface chemistry would react once
implanted. There have been several cases where currently available animal
implant models failed to replicate problems experienced in elderly patients. For
example, in elderly sick patients, the cloth on a valve sewing ring fails to heal
quickly. When a radically new fixation method was introduced that did not
employ glutaraldehyde (tradenamed PhotoFix), the increased elongation of the
tissue prepared with this new fixation method resulted in excessive tissue
abrasion and leaflet perforation within 2 years in patients, despite the fact that no
abrasion was seen during the chronic animal studies (Schoen, 1998). In another
instance of delayed cloth healing, patients implanted with Silzone-coated sewing
rings experienced higher rates of thromboembolism, infection and perivalvular
leaks than patients implanted with untreated sewing rings (Schaff et al., 2002).
In a third example, the CoreValve
Õ
percutaneous valve used in Europe has been
associated with a high incidence of heart rhythm disruption (left-bundle branch
block, LBBB). Apparently the long stent design exerts forces on critical areas in
the heart associated with normal electrical conduction, and patients fitted with
