Biomedical Engineering Reference
In-Depth Information
Cable insulation
l
Shock wave
Electrode
Bubble
+
+
+
-
-
-
-
e-
e-
-
+
+
+
T
+
+
+
Persistent current
Bubble of electrolysis gas
Voltage gradient
Increased temperature
Increased resistance
Plasma formation
Bubble expansion
Arcing
Shock wave
(c)
(a)
FIGURE 6.12
Mechanism of DC ablation. When direct current from a standard defib-
rillator is delivered to the tip of an electrode catheter, a series of events occurs, result-
ing in the generation of a shock wave. (
a
) The charge delivered to the electrode tip first
results in the electrolysis of water into hydrogen and oxygen gas. An insulating bubble
develops resulting in an increased impedance. (
b
) Current continues to flow to the tip
of the catheter despite the rise in impedance, which results in a voltage gradient across
the bubble. Arcing occurs. (
c
) Once arcing occurs, there is a tremendous rise in tem-
perature, causing the bubble to expand, generating a shock wave (
e
-
=
(b)
flow of elec-
trons). (Adapted from
Clinical Cardiology,
1990 [7].)
uation of a helical and whip antenna in a tissue-equivalent phantom was per-
formed at 915 and 2450 MHz.
As of this writing, RF cardiac ablation is the most useful technique for a
select type of arrhythmias, as discussed above. However, arrhythmias such
as atrial fibrillation and ventricular tachycardia remain difficult to treat.
Microwave ablation techniques, having deeper reach into the tissue, are cur-
rently being researched as a potential solution. As the microwave power is
coupled into the tissue volume, the electrical dipole in the tissue will oscillate
and create heat by a process known as dielectric heating.
To simulate the endocardial environment present in catheter ablation, a
flow phantom model was tested. The model consists of phantom material that
simulates cardiac muscle suspended in a saline perfusion chamber. Flow across
the surface of the phantom is controlled by a perfusion pump, thus simulating
Search WWH ::
Custom Search