Fig 1.
Geometry of the computational model built (figure not to scale).
Note that XZ-plane is the symmetry plane in the model. Cardiac tissue thickness (H) is 20 mm [4,12], while the dimensions of the fragment of cardiac chamber of X = 80 mm and Y = 40 mm (Z = Y) are estimated by means of a convergence test. Two active electrodes (8Fr, 3.5 mm) are considered (right image): 6-holes and multi-holes open-irrigated electrodes as models ThermoCool® and ThermoCool® SF (Biosense Webster, Diamond Bar, CA, USA), respectively. These are inserted into cardiac tissue a depth (DE) of 1 mm. The saline irrigation through the small holes in the electrode tip is modeled by an inlet velocity boundary condition at the electrode-blood interface. Thermal lesion is assessed by the 50°C isotherm and its geometry is characterized by: maximum depth (D), maximum width (MW), depth at the maximum width (DW), and surface width (SW).
Table 1.
Thermal and electrical characteristics of the elements employed in the numerical models (data from [17]): σ: electric conductivity; k: thermal conductivity; ρ: density; c: specific heat.
Fig 2.
Electrical (a) and thermal and velocity (b) boundary conditions of the model. Note that the effect of saline irrigation is simulated as an inlet velocity boundary condition into the blood region, since the irrigation holes are not included in the model and the saline irrigation is not considered inside the electrode.
Fig 3.
Validation of the computational model.
Experimental (data from [3]) and computational thermal lesions created in the tissue after 30 s of RFCA using power-control mode of 20 and 35 W. The thermal lesion contour was assessed by the central "white zone" in the experiments and by the 50°C isotherm in the computational model.
Table 2.
Lesion dimensions (maximum depth D, and maximum width MW) from the experimental [3] and the computational model after 30 or 60 s of RFCA using power-control mode of 20 and 35 W, with 6-holes and multi-holes open-irrigated electrodes as models ThermoCool and ThermoCool SF in [3].
The electrode was in perpendicular position respect to the cardiac tissue and the irrigation flow rate was 13 mL min-1.
Fig 4.
Effect of the irrigation flow rate: lesion dimensions (D: maximum depth, MW: maximum width, DW: depth at the maximum width, and SW: surface width) obtained after 30 s of RFA with power-control mode of 35 W, considering four irrigation flow rates (5, 10, 15 and 20 mL min-1), two designs of open-irrigated electrode tip (6-holes and multi-holes), and perpendicular and parallel electrode-tissue positions.
Fig 5.
Effect of the irrigation flow rate: temperature distributions in the cardiac tissue and blood and lesion volume (LV) after 30 s of RFCA with power-control mode of 35 W, considering four irrigation flow rates (5, 10, 15 and 20 mL min-1), two designs of open-irrigated electrode tip (6-holes and multi-holes), and perpendicular (a) and parallel (b) electrode-tissue positions. The solid black line corresponds to the 50°C isotherm. Note that the two left plots (0 mL min-1) represent the cases without saline irrigation (non-irrigated). The figure shows the saline flow velocity (Us) applied on the electrode surface in each case.
Fig 6.
Velocity field distributions for the 6-holes and multi-holes electrode with the electrode in perpendicular position respect to the tissue and considering an irrigation flow rate of 13 mL min-1.
Fig 7.
Effect of the applied power: lesion dimensions (D: maximum depth, MW: maximum width, DW: depth at the maximum width, and SW: surface width) obtained after 30 s of RFCA with power-control mode at 20, 30, 40 and 50 W, considering perpendicular and parallel electrode-tissue positions, and two designs of open-irrigated electrode tip: 6-holes (a) and multi-holes (b).
Fig 8.
Effect of the applied power: temperature distributions in the cardiac tissue and blood and lesion volume (LV) after 30 s of RFCA with power-control mode at 20, 30, 40 and 50 W, considering two designs of open-irrigated electrode tip (6-holes and multi-holes), and perpendicular (a) and parallel (b) electrode-tissue positions. The solid black line corresponds to the 50°C isotherm. The figure shows the saline flow velocity (Us) applied on the electrode surface in each case.
Fig 9.
Effect of the electrode-tissue contact pressure: (a) lesion dimensions (D: maximum depth, MW: maximum width, DW: depth at the maximum width, and SW: surface width) and (b) temperature distributions in the cardiac tissue and blood and lesion volume (LV) obtained with the multi-holes open-irrigated electrode after 30 s of RFCA considering power-control mode of 35 W (the irrigation flow rate recommended by manufacturer is 15 mL min-1), different electrode-tissue contact pressures (0.5, 0.75, 1 and 1.5 mm), and perpendicular and parallel electrode-tissue positions. The solid black line corresponds to the 50°C isotherm. The figure shows the saline flow velocity (Us) applied on the electrode surface in each case.