Biophan releases additional data on pacemaker and defibrillator lead
heating
14 May 2005
Rochester NY, USA. Biophan Technologies, Inc. (OTCBB:BIPH), has released
additional technical information on its research into pacemaker and
implantable defibrillator lead heating. The data reveal that the most
prevalent heating occurs not at the electrode tip of a lead, but actually a
short distance away from the electrode tip, in the tissue itself.
Michael Weiner, CEO of Biophan, explained: "The phenomenon we are
measuring is heat dissipation in tissue, at the interface between a highly
electrically/thermally conductive medium (the lead) and a much lower
electrically/thermally conductive medium (cardiac tissue). We have simulated
this, and are continuing to refine the computer model to account not only
for blood flow, but also the level of perfusion in the myocardium and also
in the fibrous cap that develops around the lead some time after
implantation.
"Our modeling to date indicates that heat is not created in the electrode
itself, but as the electrical energy dissipates radially from the electrode
tip and also from the helical fixation feature," said Mr. Weiner." The thin
layer of tissue in immediate contact with the lead is close enough to the
electrode that the electrode acts as a heat-sink; therefore, this thin layer
does not experience the highest degree of heating, nor does the electrode
body itself. As the current flows beyond this initial layer, the tissue is
more poorly coupled to the electrode body thermally, and thus experiences
more temperature rise. As the current flows even further outward in a radial
manner, the cross-section of tissue it transits increases, so the heating
effect falls off; in addition there is a much larger mass of tissue which
contributes to the temperature rise decreasing.
"What we see both in our computer model and in fibre-optic temperature
measurements made with highly controlled positioning fixtures, is minimal
heating of the electrode body, modest heating of the very first layer of
tissue, much higher heating slightly further out and then the temperature
increase falling off rapidly."
The new data is available on the Company's web site at:
www.biophan.com/hpgraphic.html
This additional data released on 4 May added to the data released on 29
April regarding the sensitivity of testing procedures to the probe type and
placement within the MRI bore. The company revealed that they are using a
fluorescence-based fibre optic probe in order to eliminate any electrical
interaction between the lead and measuring device which might change the
conditions at the electrode. This type of probe is consistent with the
existing ASTM Standard. Many researchers report that they use a probe that
has the sensing element in a ring around the optical fibre, which can be
located 0.5mm or more away from the end of the probe. Biophan scientists use
a probe with the sensing element at the very end, because the temperature
changes significantly over very small distances, which can be influenced by
the location of the sensing element within the probe.
Biophan also revealed that the lateral position in the MRI bore has a
significant effect on measured temperature increases. It has tested both
on-centre and slightly off-axis to simulate the degree of clinically
relevant offset that might be experienced, such as for a small individual
who is being imaged for a non-central complaint, such as a right shoulder
complaint. The degree of offset can create a much larger temperature
increase, as indicated in the data that Biophan revealed in April showing
that an offset of only several inches can result in physiologically
significant increases in lead heating of as much as 10 degrees Celsius.
"The existing ASTM Standard is somewhat qualitative regarding a) probe
positioning, b) IPG/lead positioning, and c) position within the bore; we
believe this is the reason there is such large variability in test results
for the same MRI scan sequence reported by different examiners. Given the
exponential relationship between temperature rise and the time before cell
death (one second at 60 degrees Celsius for example) we believe that safety
testing simply must be conducted over the full range of clinically relevant
conditions," Mr. Weiner concluded.
Mr. Weiner will provide the additional data at the Heart Rhythm Society's
26th Annual Scientific Sessions in New Orleans. He will be one of five
Biophan employees exhibiting and meeting with device manufacturers at the
Heart Rhythm Society session.
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