Catheter ablation of the heart using microwave energy
The heating properties of helically coiled antennas, for use in a catheter ablation system, are studied both experimentally and theoretically. A theoretical model, based on the sheath helix approximation, is presented and used to predict the antenna's specific absorption rate (SAR) pattern as a function of the geometry of the antenna and the electrical properties of the surrounding tissue. This model is then extended to include the case of an insulating layer. In addition, a thermistor based SAR mapping apparatus was constructed and used to perform experimental studies on helical antennas immersed in aqueous electrolytes of various conductivities. Analytical results agree well with the experimental data, demonstrating the validity of the model.^ For these antennas, the SAR distribution strongly reflects the presence of standing waves along the antenna. These patterns are found to be particularly sensitive to the helical pitch angle and loss in the external medium. It is shown that, by adding a thin layer of insulation to the outside of the helical antenna, one can produce a more uniform heating pattern which is insensitive to loss. This configuration appears to be suitable for catheter ablation applications.^ The microwave results are then compared to analytical and experimental results from a radio frequency (RF) ablation device. It is shown that the helical antenna offers the possibility of relatively uniform heating, whereas the RF device heats predominantly at its tip.^ In vitro experiments are performed in excised sheep hearts. Lesion sizes measured in actual tissue samples agree favorably with calculated responses. These results graphically illustrate that microwave ablation is able to produce larger lesion sizes than presently available techniques. This ability may prove useful in the catheter treatment of a variety of cardiac arrhythmias. ^
Mark Steven Mirotznik,
"Catheter ablation of the heart using microwave energy"
(January 1, 1992).
Dissertations available from ProQuest.