MILLIONS of people who wear heart pacemakers should one day be able to
undergo MRI body scans if they need to, thanks to a new type of pacemaker that
uses light rather than electricity to regulate heart rhythms.
The powerful magnetic fields used in MRI body scanners can induce dangerous
electric currents in the long wire that pacemakers use to transmit electronic
pulses from an implanted battery/electronics unit to the heart. But now Biophan,
a medical technology company in Rochester, New York, is planning to replace the
wire with an optical fibre that carries pulses of laser light.
Pacemakers are needed when the heart鈥檚 natural timer, the sino-atrial node,
fails to trigger strong regular beats. Electrical pulses generated by a
battery-powered module implanted under the skin pass through about 30
centimetres of wire to regulate the beat.
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While people with pacemakers can live normal lives, they must avoid strong
electromagnetic fields, which can induce currents in metal components. When in
shops, they should pass quickly through tag-scanning theft detection systems,
which can interfere with pacemakers. But the much higher magnetic fields used in
MRI scanners can also heat the long wire to dangerous temperatures, making MRI
unsuitable for pacemaker wearers.
Now optical fibres are coming to the rescue. They don鈥檛 conduct current so
are not prone to electromagnetic heating and interference. However, standard
laser transmitters need far more power than today鈥檚 pacemakers, which can
operate on lithium batteries for five to ten years between implants. So how can
light deliver electric power to a tiny heart-stimulating electrode?
To solve these problems, Biophan worked alongside 81-year-old Wilson
Greatbatch, who invented the original pacemaker more than 40 years ago. The
compact semiconductor laser transmitter that Biophan and Greatbatch have come up
with emits short light pulses which a tiny photocell in the fibre鈥檚 tip converts
to electricity.
So the pacemaker knows when it鈥檚 time to send a pulse, a tiny light-emitting
diode in the tip fires a short pulse down the fibre. This triggers the laser in
the pacemaker to transmit a much longer, more powerful pulse that the photocell
converts into a heart-stimulating electrical pulse.
Biophan says its first device will be a temporary pacemaker that can be used
in hospital when an implanted pacemaker is turned off and electromagnetically
shielded for an MRI scan. A spokesman expects the temporary pacemaker to be
ready for testing on people in a year鈥檚 time, with an implantable version to
follow.
An optical pacemaker 鈥渨ill be a great step forward鈥�, allowing pacemaker
patients to have an MRI scan, says Roger Luechinger, a biomedical engineer at
the Swiss Federal Institute of Technology.