In vitro experimental setup
Fresh porcine hearts were commercially obtained, which were extracted within 48 hours of sacrifice. Porcine myocardial tissue was fixed on a stage in a water pool (Figure 1). The saline solution was prepared for the water pool with 20 g of salt to 7.8 L of water so that the baseline LI was set at 90 ohms when using MiFi and 140 ohms when using STABLEPOINT because blood pool data for those catheters in the clinical setting were approximately 80–100 ohms for the MiFi and 130–150 ohms for the STABLEPOINT. The saline solution in the water pool was kept at 37 °C using a thermostatic system (Thermo-Mate BF-400, Yamato Scientific Co., Ltd., Tokyo, Japan). The water bath was circulated across the myocardial tissue surface at a flow rate of 5 L/min to simulate blood flow. The shaft of the catheter was fixed to the pillar 10 mm from the 4th ring electrode in the distal direction, and the CF on the catheter tip was measured over time by connecting the pillar to a load cell (DPU-2N, Imada Co., Ltd., Toyohashi, Japan). The voltage waveform from the load cell was recorded by a 16-bit digital coder (DP850, Yokogawa Electric Corp., Tokyo, Japan). A scale was used to calibrate the CF at the tip of the catheter with the load cell voltage value in a range of 0–30 g.