Guidelines for predicting lesion size at common endocardial locations during radio-frequency ablation

Abstract

We used the finite element method to study the effect of radio-frequency (RF) catheter ablation on tissue heating and lesion formation at different intracardiac sites exposed to different regional blood velocities. We examined the effect of application of RF current in temperature- and power-controlled mode above and beneath the mitral valve annulus where the regional blood velocities are high and low respectively. We found that for temperature-controlled ablation, more power was delivered to maintain the preset tip temperature at sites of high local blood velocity than at sites of low local blood velocity. This induced more tissue heating and larger lesion volumes than ablations at low velocity regions. In contrast, for power-controlled ablation, tissue heating was less at sites of high compared with low local blood velocity for the same RF power setting. This resulted in smaller lesion volumes at sites of low local velocity. Our numerical analyzes showed that during temperature-controlled ablation at 60 degrees C, the lesion volumes at sites above and underneath the mitral valve were comparable when the duration of RF current application was 10 s. When the duration of RF application was extended to 60 s and 120 s, lesion volumes were 33.3% and 49.4% larger above the mitral valve than underneath the mitral valve. Also, with temperature-controlled ablation, tip temperature settings of 70 degrees C or greater were associated with a risk of tissue overheating during long ablations at high local blood velocity sites. In power-controlled ablation (20 W), the lesion volume formed underneath the mitral valve was 165.7% larger than the lesion volume above the mitral valve after 10 s of ablation. We summarized the guidelines for energy application at low and high flow regions.

Comparative Analysis of Different Methods of Modeling the Thermal Effect of Circulating Blood Flow During RF Cardiac Ablation

“…The electrode was assumed to be inserted into the tissue to a depth (D E ) of 1.25 mm [14]. The model included a temperature sensor (thermistor 0.75 × 0.3 mm) embedded in the tip of the electrode, which was used for the temperature control simulation [5,14,20]. The dispersive electrode was modeled as an electrical boundary condition at a distance from the active electrode (bottom surface).…”

“…2b and 2c show the thermal and velocity boundary conditions. The effect of blood circulating inside the cardiac chamber was modeled by four methods which have been used in previous studies [3,5,[9][10][11][13][14][15]17,20,24]. Each case was assessed under conditions of high and low blood flow.…”

“…Some models do not consider blood as part of the model domain, and consequently the blood-tissue and blood-electrode interfaces were really model boundaries [3][4][5][6][7][8] on which an electrical boundary condition of zero current density was set. Other models consider blood as part of the domain [9][10][11][12][13][14][15][16][17][18][19][20][21], thus allowing RF current to flow through the blood. These models represent the initial value of the impedance (basal impedance) more realistically than those that do not include blood.…”

Could it be advantageous to tune the temperature controller during radiofrequency ablation? A feasibility study using theoretical models

“…Although previous modeling studies had assessed the effect of tissue characteristics [4], insertion depth [6,9,11], blood flow rate [5,8,9,11], electrode size [11] and temperature sensor arrangement [11][12][13][14][15] on the dimensions of the thermal lesion, some even including a PI controller in the modeling methodology [5,6,10], none had considered our hypothesis.…”

“…Certain factors are known to have an impact on lesion size, e.g. tissue characteristics [4], electrode-tissue contact characteristics [5][6][7][8][9][10], electrode size [10], arrangement [11][12][13][14] and position [15,16] of the temperature sensor embedded in the electrode. Conversely, it is also known that varying these characteristics would affect the performance of the temperature control system.…”