Sometimes things that seem like
a help can turn into a hindrance. Such is the case with
stent graft repairs of abdominal aortic aneurysms —
about 5% of them end in failure because of leaks or slippage.
But the minimally invasive procedure that saves countless
lives every year could become even more popular with a
new monitoring technique that uses wireless sensors to
make sure the stent is doing its job.
Before the arrival of stent graft
repair, management for an aortic aneurysm used to fall
in just two categories: surgical repair or "watchful
waiting," with no middle ground. Stent graft repair
revolutionized aneurysm management, but as with many
new technologies it was not without its problems.
When the FDA warned in 2001 that
stent grafts could slip or leak, it prompted doctors
to start monitoring repaired patients with annual CT
scans. But CT scans had their own risks and were often
unable to detect the smallest leaks that could cause
sudden failure of the stent.
GO
WIRELESS
Enter the wireless sensor. The sensor, which is about
the size of a quarter, is implanted into the patient
at the same time as the stent. It contains microchips
that detect pressure changes in the aneurysm. When the
patient visits the doctor's office, the doctor uses
an electric wand that receives the radio waves transmitted
by a coil antenna. Unlike CT scans, the sensor can pick
up even tiny pressure changes — changes that notify
doctors of the possibility of an imminent stent failure.
"Wireless sensors are already
used in different types of conditions," explains Dr
Andrew Krahn, a cardiologist and specialist in cardiac
monitors at the University of Western Ontario. "Intracoronary
artery patency post-stent repair is often measured by
a 'stentenna,' which detect restenosis through decreases
of blood flow from the proximal to distal parts of the
stent."
SELF-MONITORING
POTENTIAL
Patients can be regularly followed up by their physician,
or taught how to use their own monitoring equipment,
similar to self-monitoring of blood glucose in diabetics
today. "Outside of a hospital setting, there is little
that allows us to continuously monitor patients," says
Dr Krahn. "This could change, by connecting these wireless
sensors to cellular devices. Results could be assessed
in real-time, allowing us to contact the patient as
needed."
There are some concerns about
the device — the cost, risk of emboli formation
and fears it might fail to produce adequate signal —
but for the most part it seems that patients would benefit
the combined stent/sensor approach. "The aneurysm sensor
is another step in the movement to develop continuous
monitors for any number of conditions," says Dr Krahn.
The sensors have been tested
on 50 patients in the US and Brazil with very promising
results; a full-scale trial is set to begin early next
year. The sensor was developed jointly by engineers
at Georgia Institute of Technology and surgeons at the
Cleveland Clinic Foundation.
|
