Possibly related, dielectic heating of body tissue at frequencies starting at 900MHz
Ziad F. Issa MD, ... Douglas P. Zipes MD, in
Clinical Arrhythmology and Electrophysiology (Third Edition), 2019
Biophysics of Microwave Energy
Microwaves are the portion of the electromagnetic spectrum between 0.3 and 300 GHz. For the ablation of cardiac arrhythmias, microwave energy has been used at frequencies of 0.915 and 2.450 GHz. Similar to RF, microwave energy produces thermal cell necrosis. However, in contrast to heating by electrical resistance as observed during RF ablation, the mechanism of heating from a high-frequency microwave energy source is dielectrics. Dielectric heating occurs when high-frequency electromagnetic radiation stimulates the oscillation of dipolar molecules (e.g., water molecules) in the surrounding medium at a very high speed, thereby converting electromagnetic energy into kinetic energy. This high-speed vibration causes friction between water molecules within the myocardial wall that results in an increase of myocardial tissue heat. This mode of heating lends
microwave ablation the potential for a greater depth of volume heating than RF ablation and should theoretically result in a larger lesion size.86
Microwave energy is not absorbed by blood and can propagate through blood, desiccated tissue, or scar. It also can be deposited directly into the myocardial tissue at a distance, regardless of the intervening medium. The microwave energy field generated around the
ablation catheter antenna can create
myocardial lesions up to 6 to 8 mm in depth without overheating the
endocardial surface, a feature that can potentially limit the risk of charring, coagulum formation, and intramyocardial steam pops. Penetration depth achieved with microwave energy depends on several factors—dielectric properties of the tissue, frequency of the microwave energy, antenna design, and composition and thickness of the cardiac layers.86
The effectiveness of microwave ablation depends on the radiating ability of the microwave antenna that directs the electric field and determines the amount transmitted into the
myocardium, which is critical for heating. An end-firing monopolar antenna has been used to produce lesions at depths of 1 cm without disruption of the
endocardium in porcine ventricles. The depth of these lesions increased exponentially over time as compared with standard nonirrigated RF energy, which had minimal lesion expansion after 60 seconds of ablation. To concentrate more of the energy distribution near the electrode tip, circularly polarized coil antennas have been developed. Other configurations of the microwave antenna include helical, dipole, and whip designs; these have a large effect on the magnetic field created. However, many of these catheters are still under clinical investigation
