INTRODUCTIONThetissue of the human body is enormously varied and complex, with innumerabletypes of structures, components, and cells. From the point of view of RF andmicrowaves, however biological tissue can be viewed macroscopically in terms ofits bulk shape and electromagnetic characteristics. All biological tissue issomewhat electrically conductive, absorbing microwave power and converting itto heat as it penetrates the tissue.
Delivering heat at depth is not onlyvaluable for cooking dinner, but it can be quite useful for many therapeuticmedical applications as well. These include: diathermy for mild orthopedicheating, hyperthermia cell killing for cancer therapy, microwave ablation andmicrowave assisted balloon angioplasty. It should also be mentioned that basedon the long history of high power microwave exposure in humans, it isreasonably certain that, barring overheating effects, microwave radiation ismedically safe. Preliminaryexperiments on the induction of localized myocardial tissue modification bymicrowave energy without causing any cardiac arrhythmias, were the first stepin the development of an innovative procedure called microwave balloonangioplasty (MBA). MBA combines the traditional angioplasty technique withmicrowave energy to open narrowed arteries and reduce the occurrence ofrestenosis.
Microwave cardiac ablation (MCA) works by scarring and destroyingtissue in heart that triggers or sustains abnormal heart rhythm. 1.1 OBJECTIVES1. To widen thenarrowed or the obstructed arteries using a process called as “microwaveassisted balloon angioplasty (MABA)”.2. To create scarsand destroy the diseased tissues of the heart that triggers or sustainsabnormal heart rhythms using a process called as “microwave cardiac ablation”.
Chapter2 LITERATURE SURVEY2.1Balloon angioplasty :Balloon angioplasty is also known as percutaneoustransluminal angioplasty (PTA), is a minimally invasive endovascular procedureto widen the narrowed or obstructed arteries or veins.The procedure avoids cardiac bypass surgery, or other more traumaticoperations, and has been very successful at both extending and improving thequality of life 3. Procedure :Ø Aspecial catheter tipped with a collapsed narrow inflatable balloon is insertedinto the artery through an incision in the neck or leg and fed through bloodvessels until it reaches the diseased arteries of the heart. Ø Fluid(de-ionized water) is then pumped into the balloon, inflating it to severaltimes its nominal diameter. Ø Theenlarged tip quickly compresses the layer of plaque which is clogging theartery and also stretches the walls of the artery, leaving a much wider openingfor blood flow.
Ø Theballoon is then deflated and it is withdrawn along with the catheter. Ø Finallythe vessel puncture site is treated with vascular closure device. Fig1 : Balloon inserted into an artery 3 Fig 2 : Balloon angioplasty 3 Disadvantages :Ø Embolization or the launching of debris into thebloodstream.Ø Arterial rupture from over-inflation of a ballooncatheter or the use of an inappropriately large or stiff balloon.Ø Restenosis. 2.
2RF cardiac ablation :Catheter-fed ablation or excessive heating oftissue, destroys the region of the heart responsible for the anomalouselectrical activity. Radio frequency (RF) ablation, operates at frequenciesbetween 100 kHz – 10 MHz 3. Procedure:Ø More than 1 Catheter wire is guided through thearteries, to the site of lesion. Ø Mapping catheter is used to map the electricalactivities of the diseased cardiac tissue.Ø Later the co-axial RF system is inserted to createscars on the diseased cardiac tissues. Fig 3 : RF cardiac ablation 3 Disadvantages :Ø Larger lesions cannot be created by increasing thepower to the RF electrode, as this leads to tissue charring.
Ø RF ablation (100kHz – 10MHz) is generally limited toa depth of 0.5 cm, which is insufficient for eliminating deep diseased tissue. Chapter 3 METHODOLOGY1.Microwave assisted balloon angioplasty :MABAwith a helix and mode filter balloon uses the large differences in thedielectric characteristics (relative permittivity, electrical conductivity) ofhigh water content (HWC) and low water content (LWC) tissue to preferentiallyheat and weld plaque while sparing healthy artery walls.
MABA is an minimallyinvasive procedure that uses microwave (300 MHz – 300 GHz) to heat the plaquewhich makes the plaque thermally fixed in place by compressing it against theartery wall. The plaque deposition is detected by using fluoroscopy technique.MABA consists of 2 main systems, they are microwave delivery system and thecatheter system.
v Microwavedelivery system :Ø 2450MHz signal generator : A microwave signal of2450MHz frequency is generated using a signal generator.Ø Directionalcoupler : This is used to divide and distribute the power.Ø Two power meters : Here two power meters are used,one for measuring the forward power and the other one for measuring thereflected power.Ø Co-axial cable : A thin flexible co-axial cableof 0.034 diameter is used which fitswithin a conventional balloon angioplasty catheter and this co-axial cable isterminated by a radiating antenna which radiates the desired range ofmicrowaves. Ø Thermocouple : This thermocouple is used to measurethe heating temperature. v Catheter system :Ø Balloon: The catheter is tipped with an inflatable balloon which is made up of nylonor polyethylene terephthalate (PET).
Deionized water is used to inflate theballoon. Procedure :Ø Theprocedure begins by giving local anesthesia to the groin area of the leg.Ø Thenthe catheter wire is guided through the femoral artery to the site of lesion. Ø Aballoon is then guided along then guided along the wire.Ø Oncethe position of the balloon catheter is established the guide wire is removedand the same lumen is used to insert the co-axial microwave system.Ø Theballoon is then inflated and is ready to deliver the microwave energy.Ø Whenmicrowave power between 10-15 watts is delivered it takes approximately 45s forthe LWC tissue (plaque) to heat up. Ø Afterthe end of the microwave power delivery the balloon is deflated.
Ø Boththe balloon as well as the fluid (deionized water) inside the balloon arerelatively transparent to microwave energy.Ø Thenthe deflated balloon is withdrawn along with the catheter. Fig 4 : MABA applicatorconsisting of an antenna inside a catheter balloon 1 Fig: 5 (a) Fig: 5 (b) Fig : 5(c) Fig 5(a, b, c) : Procedure of MABA 3 Advantages :Ø Chancesof restenosis are less.Ø Patientcan return to normal activities shortly after the procedure.Ø Theprocedure is performed using local anesthesia, which involves fewer risks thangeneral anesthesia.
2.Microwave cardiac ablation :Microwave cardiac ablation (MCA) is an minimallyinvasive procedure that works by scarring or destroying tissues of the heartthat triggers or sustains abnormal heart rhythms. MCA is used to treat hearttissues that allow abnormal electrical conduction by heating it to the point ofinactivation. Microwave antenna that fits within the catheter system can bepositioned close to the diseased tissue. MCA is an important procedure used tocorrect heart rhythm problems (arrthymia).
Procedure:Ø Theprocedure begins by giving local anesthesia to the point where the catheter isbeing inserted.Ø In microwave cardiac ablation catheter are insertedthrough the arteries in order to reach the heart. Catheters may be insertedthrough groin, shoulder or through neck. Ø More than 1 Catheter wire is guided through thearteries, to the site of lesion.
Ø Mapping catheter is used to map the electricalactivities of the diseased cardiac tissue.Ø Later the co-axial microwave system is inserted tocreate scars on the diseased cardiac tissues.Ø Once the procedure is completed the mapping as wellas the ablation catheters are removed.Ø The punctured site is ten treated with either directpressure or vascular closure device. Fig 6 : Points from where catheter can be inserted 3 Fig 7 3 : Ablation Catheter Fig 7 (A, B) : Microwave cardiac ablation 3 Advantages :Ø Canlessen or eliminate the heart rhythm problems.Ø Allowsto decrease or stop long term medications for heart rhythm problems. Chapter- 4 Conclusion Ø Inmicrowave balloon angioplasty (MABA) the plaque was heated and compressedagainst the arterial walls using microwave delivery system and catheter.
Andalso microwaves were more advantageous than RF waves.Ø Inmicrowave cardiac ablation (MCA), microwave catheters were used to create scarson the diseased tissue that were responsible for abnormal heart rhythms. REFERENCES 1. Carey Rappaport , “Treating cardiacdisease with catheter – based tissue heating”, USA, IEEE.2. Rosen, Thomas Jefferson, “Microwaveballoon angioplasty”, Baxter Healthcare Corporation, Edwards LIS Division,Irvine California, USA.