tissue of the human body is enormously varied and complex, with innumerable
types of structures, components, and cells. From the point of view of RF and
microwaves, however biological tissue can be viewed macroscopically in terms of
its bulk shape and electromagnetic characteristics. All biological tissue is
somewhat electrically conductive, absorbing microwave power and converting it
to heat as it penetrates the tissue. Delivering heat at depth is not only
valuable for cooking dinner, but it can be quite useful for many therapeutic
medical applications as well. These include: diathermy for mild orthopedic
heating, hyperthermia cell killing for cancer therapy, microwave ablation and
microwave assisted balloon angioplasty. It should also be mentioned that based
on the long history of high power microwave exposure in humans, it is
reasonably certain that, barring overheating effects, microwave radiation is
experiments on the induction of localized myocardial tissue modification by
microwave energy without causing any cardiac arrhythmias, were the first step
in the development of an innovative procedure called microwave balloon
angioplasty (MBA). MBA combines the traditional angioplasty technique with
microwave energy to open narrowed arteries and reduce the occurrence of
restenosis. Microwave cardiac ablation (MCA) works by scarring and destroying
tissue in heart that triggers or sustains abnormal heart rhythm.
To widen the
narrowed or the obstructed arteries using a process called as “microwave
assisted balloon angioplasty (MABA)”.
To create scars
and destroy the diseased tissues of the heart that triggers or sustains
abnormal heart rhythms using a process called as “microwave cardiac ablation”.
Balloon angioplasty :
Balloon angioplasty is also known as percutaneous
transluminal angioplasty (PTA), is a minimally invasive endovascular procedure
to widen the narrowed or obstructed arteries or veins.
The procedure avoids cardiac bypass surgery, or other more traumatic
operations, and has been very successful at both extending and improving the
quality of life 3.
special catheter tipped with a collapsed narrow inflatable balloon is inserted
into the artery through an incision in the neck or leg and fed through blood
vessels until it reaches the diseased arteries of the heart.
(de-ionized water) is then pumped into the balloon, inflating it to several
times its nominal diameter.
enlarged tip quickly compresses the layer of plaque which is clogging the
artery and also stretches the walls of the artery, leaving a much wider opening
for blood flow.
balloon is then deflated and it is withdrawn along with the catheter.
the vessel puncture site is treated with vascular closure device.
1 : Balloon inserted into an artery 3
Fig 2 : Balloon angioplasty 3
Ø Embolization or the launching of debris into the
Ø Arterial rupture from over-inflation of a balloon
catheter or the use of an inappropriately large or stiff balloon.
RF cardiac ablation :
Catheter-fed ablation or excessive heating of
tissue, destroys the region of the heart responsible for the anomalous
electrical activity. Radio frequency (RF) ablation, operates at frequencies
between 100 kHz – 10 MHz 3.
Ø More than 1 Catheter wire is guided through the
arteries, to the site of lesion.
Ø Mapping catheter is used to map the electrical
activities of the diseased cardiac tissue.
Ø Later the co-axial RF system is inserted to create
scars on the diseased cardiac tissues.
Fig 3 : RF cardiac ablation 3
Ø Larger lesions cannot be created by increasing the
power to the RF electrode, as this leads to tissue charring.
Ø RF ablation (100kHz – 10MHz) is generally limited to
a depth of 0.5 cm, which is insufficient for eliminating deep diseased tissue.