A novel three-dimensional finite element model for the study of radiofrequency ablation is presented. The model was used to perform an analysis of the temperature distribution in a tissue block heated by RF energy and cooled by blood (fluid) flow. This work extends earlier models by including true flow in place of a convective boundary condition to simulate realistic experimental conditions and to improve the prediction of blood temperatures. The effect of fluid flow on the temperature distribution, the lesion dimensions, and the ablation efficiency was studied. Three flow velocities were simulated: (i) 30, (ii) 55, and (iii) 85 mm/s. The modeling results were validated qualitatively and quantitatively with in vitro data. The correlation coefficients between the modeling and the experimental temperature measurements were 0.98, 0.97, and 0.95 for flows (i)-(iii), respectively. The slopes were 0.89, 0.95, and 1.06, and the mean root mean square differences between modeling and experimental temperature measurements were 17.3% +/- 11.6%, 15.8% +/- 13.4%, and 18.8% +/- 14.9% for flows (i)-(iii), respectively. A comparison of temperature distribution obtained with a convective boundary versus inclusion of fluid motion showed that the convective boundary resulted in a similar tissue temperature distribution, but overestimated fluid temperatures and lacked the flow asymmetry seen in the true flow model.

Radio-frequency (RF) catheter ablation is the primary interventional therapy for the treatment of many cardiac tachyarrhythmias. Three-dimensional finite element analysis of constant-power (CPRFA) and temperature-controlled RF ablation (TCRFA) of the endocardium is performed. The objectives are to study: 1) the lesion growth with time and 2) the effect of ground electrode location on lesion dimensions and ablation efficiency. The results indicate that: a) for TCRFA: i) lesion growth was fastest during the first 20 s, subsequently the lesion growth slowed reaching a steady state after 100 s, ii) positioning the ground electrode directly opposite the catheter tip (optimal) produced a larger lesion, and iii) a constant tip temperature maintained a constant maximum tissue temperature; b) for CPRFA: i) the lesion growth was fastest during the first 20 s and then the lesion growth slowed; however, the lesion size did not reach steady state even after 600 s suggesting that longer durations of energy delivery may result in wider and deeper lesions, ii) the temperature-dependent electrical conductivity of the tissue is responsible for this continuous lesion growth, and iii) an optimal ground electrode location resulted in a slightly larger lesion and higher ablation efficiency.

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This paper presents an in vitro temperature mapping study of bovine cardiac tissue during radiofrequency ablation. The objectives were to: (i) develop a technique for measuring the spatial and temporal temperature distribution in the tissue and in the blood during ablation, and (ii) use the temperature measurements to characterize the effects of fluid flow on lesion dimensions, ablation efficiency, and temperature distributions. In vitro ablation (20 W, 60 s) of bovine cardiac tissue was performed. The tissue was placed in a saline-dextrose solution maintained at 37+/- 0.5 degrees C. The solution also irrigated the tissue surface and simulated blood flow velocities of (i) 30, (ii) 55, and (iii) 85 mm/s. Thermocouple measurements were recorded from 25 and 2 locations in the tissue and in the fluid, respectively. The lowest flow resulted in the largest lesion, the maximum tissue, fluid, and electrode temperature increases, and the highest ablation efficiency. The lesions were 5.8 +/- 0.81, 4.8 +/- 0.84, and 4.4 +/- 1.25 mm deep, and 9.3 +/- 1.07, 7.9 +/- 1.48, and 7.8 +/- 1.27 mm wide for flows (i)-(iii), respectively. The blood and tissue temperature distributions were asymmetric around the ablating electrode axis with higher temperatures on the outflow than on the inflow side. The experimental measurements were used to validate a numeric model of ablation in an accompanying paper.

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The simultaneous delivery of phase-shifted, radiofrequency energy using a multipolar catheter is more effective and efficient in producing linear lesions than the traditional drag-and-burn technique. Using the multipolar ablative method to create linear lesions may be a useful technique in the treatment of patients with substrate-mediated atrial fibrillation.