Computational Modeling of Open-Irrigated Electrodes for Radiofrequency Cardiac Ablation Including Blood Motion-Saline Flow Interaction

Abstract

Radiofrequency catheter ablation (RFCA) is a routine treatment for cardiac arrhythmias. During RFCA, the electrode-tissue interface temperature should be kept below 80°C to avoid thrombus formation. Open-irrigated electrodes facilitate power delivery while keeping low temperatures around the catheter. No computational model of an open-irrigated electrode in endocardial RFCA accounting for both the saline irrigation flow and the blood motion in the cardiac chamber has been proposed yet. We present the first computational model including both effects at once. The model has been validated against existing experimental results. Computational results showed that the surface lesion width and blood temperature are affected by both the electrode design and the irrigation flow rate. Smaller surface lesion widths and blood temperatures are obtained with higher irrigation flow rate, while the lesion depth is not affected by changing the irrigation flow rate. Larger lesions are obtained with increasing power and the electrode-tissue contact. Also, larger lesions are obtained when electrode is placed horizontally. Overall, the computational findings are in close agreement with previous experimental results providing an excellent tool for future catheter research.

Computational Model for Prediction the Occurrence of Steam Pops during Irrigated Radiofrequency Catheter Ablation

“…The electrode is endowed with a sensor embedded in its tip for temperature monitoring. We consider, besides the open-irrigated electrode (8Fr diameter and 3.5 mm length) with 6-holes presented in [3], a multi-holes electrode with 56-holes distributed around its entire distal tip [4] (see Figure 1 for the perpendicular positioning). These designs of electrodes represent two available commercial catheters for RFCA: ThermoCool ® (6-holes) and ThermoCool SF ® (56-holes), both from Biosense Webster (Diamond Bar, CA, USA).…”

“…The flowing saline mixes with the circulating blood without forming a film around the electrode. The effect of saline flow is modeled as an inlet boundary condition into the blood region, set at the zone where the holes are located (see violet surface in Figure 1) [4].…”

“…The thermal and electrical properties of the model elements are obtained from [4]. The initial model temperature is 37ºC, except in the electrode tip which is 22ºC, imposed as a consequence of the saline irrigation.…”

“…The initial model temperature is 37ºC, except in the electrode tip which is 22ºC, imposed as a consequence of the saline irrigation. The electrical (σ) and thermal conductivity (k) of cardiac tissue are temperature-dependent and are defined by piecewise functions as described in [4]. Figure 1.…”

“…The governing equation for the thermal problem is the Bioheat Equation, modified by the enthalpy method [4] that includes the phase change to model tissue vaporization:…”