Biomedical Engineering Reference
In-Depth Information
Absence of migration
After complete implantation, the prosthesis migrated to some extent six
times in 35 deliveries. The reasons for this complication were well under-
stood in each case. A proper solution was also found when needed and
underlines the fact that this complication is well controlled by the prosthesis
design. The six migratory events were as follows:
1. The catheter tip, insuffi ciently smooth, hooked the prosthesis upon
retrieval. Modifi cation of the tip geometry resolved this problem and
further events were avoided.
2. Bearing in mind that these were fi rst generation devices, there was some
variation in materials present. In particular, in this case the prosthesis
was made out of a metal wire that was smaller (0.014 inch (0.36 mm)
diameter) and therefore supplied insuffi cient radial force. Following this
encounter, frames with at least one element with a thicker wire
(0.016 inch (0.41 mm) diameter), and therefore a higher radial force,
were used.
3. The part of the prosthesis intended to anchor on the valve annulus was
made of a smaller wire (0.014 inch diameter). After this implantation,
the whole frame was made with thicker wire (0.016 inch diameter).
4. Measurements of the valve annulus (25 mm) and the ascending aorta
(30 mm) showed that the prosthesis that was available would be signifi -
cantly undersized. No other CoreValve prosthesis was then available. It
was nonetheless decided to implant in order to document the conse-
quences of the anticipated migration.
5. The prosthesis was precisely implanted under echocardiographic guid-
ance, but migrated upon return to normal blood fl ow. This was again
due to insuffi cient radial force.
6. The angioplasty procedure combined with blood pressure over the
balloon led to migration of the prosthesis.
These six cases of prosthesis migration, although highlighting one of the
perceived limitations and challenges associated with this new technology,
resulted in both modifi cation to the technology itself, and better informed
deployment techniques prior to moving to studies in the clinical setting.
Free coronary fl ow
Ninety-four percent of implanted prosthesis showed free coronary blood
fl ow. This was assessed by angiography and the absence of ECG changes.
It was clear from these investigations that the prosthesis design does not
alter the coronary perfusion following delivery and in the hours immedi-
ately after implantation.
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