Pacing and Ablation Technique Using Microelectrode for Pulmonary Vein Isolation Using a Local Impedance‐Guided Catheter
Introduction Pulmonary veins (PVs) contribute to the triggers and substrate of atrial fibrillation (AF), and pulmonary vein isolation (PVI) has become the cornerstone strategy for the treatment of AF . Reconnections of the PVs are related to arrhythmia recurrence, and a durable PVI is essential for achieving good procedural outcomes . An index‐guided ablation, such as with the ablation index, force‐time integral, or lesion index, contributes to an improvement in the success rate of the procedures by enabling the prediction of the lesion size . However, those indices have difficulty predicting steam pops, which are related to cardiac tamponade . Recently, the local impedance (LI) has emerged as a novel approach to detect catheter‐tissue coupling and assess the time‐dependent changes in the lesion formation during the RF energy delivery . The IntellaNav MiFi OI (“MiFi,” Boston Scientific) and IntellaNav STABLEPOINT (Boston Scientific) are available for monitoring the LI. The MiFi catheter is equipped with three miniature‐electrodes that allow electrical potentials at ablation sites. However, the MiFi catheter does not have a contact force (CF) sensor, which is crucial for predicting the ablation lesion size, making it challenging to perform a circumferential PVI. Additionally, the MiFi catheter is not equipped with ablation indices, further complicating the determination of the optimal ablation time based on index‐guided parameters. The mini‐electrodes on the MiFi catheter are independent of the ablation electrodes, allowing for ablation under local pacing, suggesting the potential usefulness as an indicator for local electrical conduction block. In this study, we investigated the target LI values for a successful PVI under the pacing and ablation technique using the MiFi catheter.   Methods 2.1 Study Patients Twenty‐seven consecutive AF patients, who underwent a first AF ablation using MiFi catheters, were enrolled in this study. This study was performed in accordance with the provisions of the Declaration of Helsinki and local regulations. The research protocol was approved by the hospital's institutional review board(#20‐165). 2.2 Ablation Procedure All antiarrhythmic agents were discontinued for at least 5 half‐lives prior to the ablation. All ablation procedures were performed under deep sedation using propofol, dexmedetomidine, and pentazocine. The bispectral index was monitored and maintained at 40–60. Using a 3D mapping system (Rhythmia, Boston Scientific) and a small basket array with 64 mini‐electrodes (IntellaMap Orion, Boston Scientific), the geometry of the left atrium (LA) and PVs were created after the approach to the LA. Before the PVI, an electrical cardioversion was performed to recover sinus rhythm in cases in which AF persisted. One patient, whose AF did not terminate by electrical cardioversion, was excluded from this analysis. Under the 3D mapping guide, the PVI was performed using the MiFi catheter and a steerable sheath (Agilis, Abbott). Pacing during the radiofrequency (RF) application was performed from the miniature‐electrodes that recorded the sharpest potential, which was considered to be in contact with the local tissue (Figure ). Effective RF applications were defined as the loss of pacing capture (Figure ), and an additional 10 s of ablation after the capture loss was set as the endpoint for each ablation site while performing a circumferential PVI. At the sites where stimulation from any of the electrodes did not capture the atrium, a 20‐s application was performed, and at the sites where capture loss was not achieved, a 30‐s ablation was performed. The MiFi catheter has an ablation tip length of 4.5 mm, and the longer tip electrode loses electrical current to the blood pool. A relatively higher power is needed for lesion formation , so ablation was performed with a power of 40 W. An esophageal thermometer (Esophaster, Japan Lifeline) was inserted. If the temperature of the esophagus reached 41°C, the RF application was ceased on the posterior wall area adjacent to the esophagus for safety concerns. PVI was confirmed by demonstrating both entrance and exit block. Entrance block was defined as the disappearance of PV potentials recorded from catheters placed in each PV. Exit block was assessed using a pacing maneuver performed with catheters positioned in each PV. For cases in which a PVI was not achieved after ablation, mapping was performed using the Orion catheter to locate gaps, and ablation was added until the electrical isolation was achieved. If the earliest activation was observed in the carina area, suggesting an epicardial connection, additional RF application was performed at the discretion of the physician. After a waiting time of at least 15 min, 2 µg of isoproterenol (ISP) and 20 mg of adenosine triphosphate were administered intravenously to confirm the presence of any dormant conduction. The sites with dormant conduction were also defined as the gap sites. All PV areas were divided into 16 segments (eight areas for each PV) and 4 segments (anterior area and posterior area for each PV) (Figure ), and the distribution of the gaps was evaluated. 2.3 Impedance Analysis The MiFi catheter measures the LI between the three miniature electrodes on the catheter tip and the proximal ring of the ablation catheter. The LI was assessed at the beginning of ablation (initial LI), at the time of pacing capture loss, and at the end of the ablation. The LI drop from the initial LI up to capture loss and the end of the ablation were evaluated as the %LI drop by dividing those values by the initial LI (Figure ). The generator impedance (GI) was also assessed at the same timings. Before the energy delivery, the radiofrequency value of the MiFi catheter is set at 46 kHz for the measurement of the LI, and after the energy delivery, it increases to 460kHz. Due to the frequency change after the energy delivery, the GI of the MiFi catheter exhibited a rapid decrease followed by a gradual decline (Figure ) . The initial GI was measured as the value of the GI that began to decrease immediately after the frequency change. 2.4 Statistical Analysis The statistical analyses were performed using Prism (GraphPad Prism9, GraphPad Software Inc., San Diego, CA) and Python (Python 3.11.0) software. The parametric data are expressed as the mean ± SD and non‐parametric data as the median with the IQR. The continuous variables were compared using a t ‐test for parametric data and Mann–Whitney test for non‐parametric data. The categorical data were compared by a chi‐square test. Two‐sided p values < 0.05 were considered statistically significant.   Study Patients Twenty‐seven consecutive AF patients, who underwent a first AF ablation using MiFi catheters, were enrolled in this study. This study was performed in accordance with the provisions of the Declaration of Helsinki and local regulations. The research protocol was approved by the hospital's institutional review board(#20‐165).   Ablation Procedure All antiarrhythmic agents were discontinued for at least 5 half‐lives prior to the ablation. All ablation procedures were performed under deep sedation using propofol, dexmedetomidine, and pentazocine. The bispectral index was monitored and maintained at 40–60. Using a 3D mapping system (Rhythmia, Boston Scientific) and a small basket array with 64 mini‐electrodes (IntellaMap Orion, Boston Scientific), the geometry of the left atrium (LA) and PVs were created after the approach to the LA. Before the PVI, an electrical cardioversion was performed to recover sinus rhythm in cases in which AF persisted. One patient, whose AF did not terminate by electrical cardioversion, was excluded from this analysis. Under the 3D mapping guide, the PVI was performed using the MiFi catheter and a steerable sheath (Agilis, Abbott). Pacing during the radiofrequency (RF) application was performed from the miniature‐electrodes that recorded the sharpest potential, which was considered to be in contact with the local tissue (Figure ). Effective RF applications were defined as the loss of pacing capture (Figure ), and an additional 10 s of ablation after the capture loss was set as the endpoint for each ablation site while performing a circumferential PVI. At the sites where stimulation from any of the electrodes did not capture the atrium, a 20‐s application was performed, and at the sites where capture loss was not achieved, a 30‐s ablation was performed. The MiFi catheter has an ablation tip length of 4.5 mm, and the longer tip electrode loses electrical current to the blood pool. A relatively higher power is needed for lesion formation , so ablation was performed with a power of 40 W. An esophageal thermometer (Esophaster, Japan Lifeline) was inserted. If the temperature of the esophagus reached 41°C, the RF application was ceased on the posterior wall area adjacent to the esophagus for safety concerns. PVI was confirmed by demonstrating both entrance and exit block. Entrance block was defined as the disappearance of PV potentials recorded from catheters placed in each PV. Exit block was assessed using a pacing maneuver performed with catheters positioned in each PV. For cases in which a PVI was not achieved after ablation, mapping was performed using the Orion catheter to locate gaps, and ablation was added until the electrical isolation was achieved. If the earliest activation was observed in the carina area, suggesting an epicardial connection, additional RF application was performed at the discretion of the physician. After a waiting time of at least 15 min, 2 µg of isoproterenol (ISP) and 20 mg of adenosine triphosphate were administered intravenously to confirm the presence of any dormant conduction. The sites with dormant conduction were also defined as the gap sites. All PV areas were divided into 16 segments (eight areas for each PV) and 4 segments (anterior area and posterior area for each PV) (Figure ), and the distribution of the gaps was evaluated.   Impedance Analysis The MiFi catheter measures the LI between the three miniature electrodes on the catheter tip and the proximal ring of the ablation catheter. The LI was assessed at the beginning of ablation (initial LI), at the time of pacing capture loss, and at the end of the ablation. The LI drop from the initial LI up to capture loss and the end of the ablation were evaluated as the %LI drop by dividing those values by the initial LI (Figure ). The generator impedance (GI) was also assessed at the same timings. Before the energy delivery, the radiofrequency value of the MiFi catheter is set at 46 kHz for the measurement of the LI, and after the energy delivery, it increases to 460kHz. Due to the frequency change after the energy delivery, the GI of the MiFi catheter exhibited a rapid decrease followed by a gradual decline (Figure ) . The initial GI was measured as the value of the GI that began to decrease immediately after the frequency change.   Statistical Analysis The statistical analyses were performed using Prism (GraphPad Prism9, GraphPad Software Inc., San Diego, CA) and Python (Python 3.11.0) software. The parametric data are expressed as the mean ± SD and non‐parametric data as the median with the IQR. The continuous variables were compared using a t ‐test for parametric data and Mann–Whitney test for non‐parametric data. The categorical data were compared by a chi‐square test. Two‐sided p values < 0.05 were considered statistically significant.   Results 3.1 Clinical Characteristics and Ablation Points Table shows the baseline characteristics in this study. A first‐pass isolation was obtained in 22 patients (84.6 %) for the left PVs and 15 patients (57.7 %) for the right PVs. Ablation was performed at 727 points for the left PVs and 859 points for the right PVs. Points where pacing did not capture (left PVs, n = 211; right PVs, n = 222), capture loss could not be confirmed (left PVs, n = 8; right PVs, n = 4), and additional carina ablation (left PVs, n = 14; right PVs, n = 45), were excluded from the analysis. The remaining 494 points (left PVs) and 588 points (right PVs) were analyzed. Figure shows the distribution of the gap sites in the PVI areas. Touch‐up ablation was needed at 8 points (1.6%) for the left PVs and 28 points (4.8%) for the right PVs. The anterior‐superior area of the left PVs and the roof of the right PVs were popular sites of gap formation. 3.2 Impedance Changes During the RF Application Figure shows the impedance changes and % impedance changes at each ablation timing. Except for the GI changes between the capture loss and ablation end on the posterior wall, the LI and GI significantly decreased throughout the time (Figure upper panel, Table ). The %LI drop was significantly greater than the %GI drop (Figure lower panel, Table ). 3.3 Prediction of Ablation Gaps Figure shows the difference in the ablation time and impedance changes at the ablation end between the gap sites and non‐gap sites. Although the capture loss time and ablation time did not exhibit significant differences (non‐gap sites vs. gap sites; capture loss time, 5.5 [±4.1] vs. 6.1 [±3.9] s, p = 0.3945; ablation time, 14.8 [±5.2] vs. 15.8 [±4.1] s, p = 0.2653), the non‐gap sites had statistically higher impedance drops and % impedance drops than the gap sites (non‐gap sites vs. gap sites; LI drop, 23.2 [±10.3] vs. 15.6 [±7.7] Ω, p < 0.0001; GI drop, 4.8 [±4.1] vs. 2.7 [±3.9] Ω, p = 0.0026; %LI drop, −19.3 [±7.4] vs. −13.1 [±6.1] %, p < 0.0001; % GI drop, −5.1 [±4.2] vs. −2.9 [±4.2] %, p = 0.0020). Figure shows the ROC analysis for gaps versus impedance changes. The LI drop AUC was 0.72064, with optimal performance at a 15 Ω drop (sensitivity 0.6111, 1‐specificity 0.2539); the %LI drop AUC was 0.73769, best at a −13.74% drop (sensitivity 0.6389, 1‐specificity 0.2539); the GI drop AUC was 0.64990, highest at a 5 Ω drop (sensitivity 0.8611, 1‐specificity 0.6049); and the %GI drop AUC was 0.65905, greatest at a −5.1546% drop (sensitivity 0.8056, 1‐specificity 0.5133), respectively. Regarding the gap prediction, the AUC for the LI was larger than that for the GI.   Clinical Characteristics and Ablation Points Table shows the baseline characteristics in this study. A first‐pass isolation was obtained in 22 patients (84.6 %) for the left PVs and 15 patients (57.7 %) for the right PVs. Ablation was performed at 727 points for the left PVs and 859 points for the right PVs. Points where pacing did not capture (left PVs, n = 211; right PVs, n = 222), capture loss could not be confirmed (left PVs, n = 8; right PVs, n = 4), and additional carina ablation (left PVs, n = 14; right PVs, n = 45), were excluded from the analysis. The remaining 494 points (left PVs) and 588 points (right PVs) were analyzed. Figure shows the distribution of the gap sites in the PVI areas. Touch‐up ablation was needed at 8 points (1.6%) for the left PVs and 28 points (4.8%) for the right PVs. The anterior‐superior area of the left PVs and the roof of the right PVs were popular sites of gap formation.   Impedance Changes During the RF Application Figure shows the impedance changes and % impedance changes at each ablation timing. Except for the GI changes between the capture loss and ablation end on the posterior wall, the LI and GI significantly decreased throughout the time (Figure upper panel, Table ). The %LI drop was significantly greater than the %GI drop (Figure lower panel, Table ).   Prediction of Ablation Gaps Figure shows the difference in the ablation time and impedance changes at the ablation end between the gap sites and non‐gap sites. Although the capture loss time and ablation time did not exhibit significant differences (non‐gap sites vs. gap sites; capture loss time, 5.5 [±4.1] vs. 6.1 [±3.9] s, p = 0.3945; ablation time, 14.8 [±5.2] vs. 15.8 [±4.1] s, p = 0.2653), the non‐gap sites had statistically higher impedance drops and % impedance drops than the gap sites (non‐gap sites vs. gap sites; LI drop, 23.2 [±10.3] vs. 15.6 [±7.7] Ω, p < 0.0001; GI drop, 4.8 [±4.1] vs. 2.7 [±3.9] Ω, p = 0.0026; %LI drop, −19.3 [±7.4] vs. −13.1 [±6.1] %, p < 0.0001; % GI drop, −5.1 [±4.2] vs. −2.9 [±4.2] %, p = 0.0020). Figure shows the ROC analysis for gaps versus impedance changes. The LI drop AUC was 0.72064, with optimal performance at a 15 Ω drop (sensitivity 0.6111, 1‐specificity 0.2539); the %LI drop AUC was 0.73769, best at a −13.74% drop (sensitivity 0.6389, 1‐specificity 0.2539); the GI drop AUC was 0.64990, highest at a 5 Ω drop (sensitivity 0.8611, 1‐specificity 0.6049); and the %GI drop AUC was 0.65905, greatest at a −5.1546% drop (sensitivity 0.8056, 1‐specificity 0.5133), respectively. Regarding the gap prediction, the AUC for the LI was larger than that for the GI.   Discussion 4.1 Major Findings The major findings of our study are summarized below: (1) Despite the MiFi catheter lacking a CF sensor, the pacing and ablation technique was suggested to have potential utility for the PVI. (2) Both the LI and GI decreased throughout ablation. The LI changes exhibited a greater change than the GI changes. (3) Although there was no statistical significance regarding the capture loss time between the non‐gap sites and gap sites, the impedance drop at the gap sites was smaller than that at the non‐gap sites, suggesting that changes in the impedance could be useful for predicting gaps. (4) The LI was more effective than the GI in predicting gaps. The cutoff values for predicting no gaps were identified as 15.0 Ω for the LI drop and −13.74% for the %LI drop, respectively. 4.2 Utility of the Pacing and Ablation Method for the PVI The pacing and ablation technique with a non‐CF catheter has been previously reported ; however, the previous report used pacing for verification of conduction block after the ablation. The circumferential ablation performed under pacing was novel in our study. The procedural time in a previous study was about 180 min, which is longer than that in our study. Performing the energy delivery while confirming the local conduction block under pacing contributed to minimizing any excessive energy deliveries and gap formation, leading to a reduction in the procedural time. A previous study on the utility of the PVI using the StablePoint catheter, which allows for CF monitoring, reported that the first‐pass isolation rates were 75.3% for the left PVs and 69.3% for the right PVs . Although the MiFi catheter lacks a CF sensor, by employing the pacing and ablation techniques, we achieved relatively similar first‐pass isolation rates of 84.6% for the left PVs and 57.7% for the right PVs. Although we did not use the LI information for the ablation endpoint in this study, incorporating the impedance information at the ablation endpoint could potentially increase the first‐pass isolation rates. Furthermore, the tip length of the MiFi catheter is 4.5 mm, leading to a relatively greater loss of energy into the blood pool as compared with the StablePoint catheter. Therefore, utilizing an output higher than 40 W could also potentially enhance the first‐pass isolation outcomes. 4.3 Impedance Changes During the RF Application Achieving a loss of excitability at each ablation site is essential for a PVI, yet there were no significant differences in the capture loss time and ablation time in this study. Irreversible loss of excitability is observed at temperatures above 50°C, but reversible loss of excitability can occur even at 50°C . Therefore, even if a temporary capture loss is achieved, it may not indicate the irreversible loss of excitability and the creation of a transmural lesion, potentially leading to gaps, which suggests that capture loss time may not be helpful for predicting conduction gaps. On the other hand, impedance changes reflecting the delivery of electrical current to local tissues are linked to changes in tissue temperature, and seem to be useful for predicting the formation of transmural lesions. Changes in the GI have been reported as an indicator of an effective electrical delivery . A drop in the GI correlates with the lesion size, and excessive drops have been linked to steam pops. Indeed, in this study, the GI decreased throughout the ablation process. However, as shown in Table , both the value and the rate of change in the GI drop were smaller than that of the LI. Moreover, the GI is subject to variability due to factors like body weight or lung influence, presenting limitations. Conversely, the LI provides specific impedance information at the tissue‐electrode contact surface, reflecting the electrical coupling between the catheter and tissue, and correlates with the local tissue temperature. A decrease in the LI during RF energy delivery correlates more closely with the lesion size than either the force‐time index or GI drops . Given that the rate of change in the LI drop is significantly greater at any point during ablation than the decrease in the GI, the LI can offer more excellent utility for monitoring during ablation procedures than the GI. 4.4 Prediction of Ablation Gaps From the Impedance Changes Our study suggested that impedance changes were useful for predicting gaps, and compared to the GI, the LI was more sensitive to gap formation than GI. The LI obtains impedance information at the tissue‐electrode contact surface, which results in greater utility in predicting gaps than the GI. Previous reports have suggested an LI cutoff value for predicting gaps with the MiFi catheter between 12.3 and 16.1 Ω . In the present study, although a higher power setting than the previous study was applied, a similar LI cutoff value for gap prediction (15.0 Ω) was observed. On the other hand, we previously reported that the LI cutoff value for gap prediction using the StablePoint was 20.0 Ω, which was higher than that in the present study . This discrepancy might be attributed to the larger measurement distance for the LI with the STABLEPOINT (9.3 mm) as compared to the MiFi (7.5 mm), resulting in larger changes in the LI and, consequently, a higher cutoff value for the gaps in the StablePoint . 4.5 Limitations Our study had several limitations. First, due to the relatively small number of cases studied, further investigation with a larger sample size is necessary. Second, our study focused on the acute effects and did not assess outcomes during the chronic phase. The findings may differ if evaluated in the chronic phase, and the cutoff value for predicting gaps during that phase remains unclear. Third, pulse field ablation (PFA) is a new technology that has been widely adopted in catheter ablation in recent years and has the potential to become the mainstream technique for first session PVI. In PFA ablation, even reversible electroporation caused by insufficient PFA application can result in capture loss in the acute phase. Therefore, our method may only be applicable to RF ablation. Finally, the LI and the capture threshold can vary depending on the angle of the catheter, and this analysis did not take the catheter angle into consideration . The cutoff value may change depending on the catheter angle.   Major Findings The major findings of our study are summarized below: (1) Despite the MiFi catheter lacking a CF sensor, the pacing and ablation technique was suggested to have potential utility for the PVI. (2) Both the LI and GI decreased throughout ablation. The LI changes exhibited a greater change than the GI changes. (3) Although there was no statistical significance regarding the capture loss time between the non‐gap sites and gap sites, the impedance drop at the gap sites was smaller than that at the non‐gap sites, suggesting that changes in the impedance could be useful for predicting gaps. (4) The LI was more effective than the GI in predicting gaps. The cutoff values for predicting no gaps were identified as 15.0 Ω for the LI drop and −13.74% for the %LI drop, respectively.   Utility of the Pacing and Ablation Method for the PVI The pacing and ablation technique with a non‐CF catheter has been previously reported ; however, the previous report used pacing for verification of conduction block after the ablation. The circumferential ablation performed under pacing was novel in our study. The procedural time in a previous study was about 180 min, which is longer than that in our study. Performing the energy delivery while confirming the local conduction block under pacing contributed to minimizing any excessive energy deliveries and gap formation, leading to a reduction in the procedural time. A previous study on the utility of the PVI using the StablePoint catheter, which allows for CF monitoring, reported that the first‐pass isolation rates were 75.3% for the left PVs and 69.3% for the right PVs . Although the MiFi catheter lacks a CF sensor, by employing the pacing and ablation techniques, we achieved relatively similar first‐pass isolation rates of 84.6% for the left PVs and 57.7% for the right PVs. Although we did not use the LI information for the ablation endpoint in this study, incorporating the impedance information at the ablation endpoint could potentially increase the first‐pass isolation rates. Furthermore, the tip length of the MiFi catheter is 4.5 mm, leading to a relatively greater loss of energy into the blood pool as compared with the StablePoint catheter. Therefore, utilizing an output higher than 40 W could also potentially enhance the first‐pass isolation outcomes.   Impedance Changes During the RF Application Achieving a loss of excitability at each ablation site is essential for a PVI, yet there were no significant differences in the capture loss time and ablation time in this study. Irreversible loss of excitability is observed at temperatures above 50°C, but reversible loss of excitability can occur even at 50°C . Therefore, even if a temporary capture loss is achieved, it may not indicate the irreversible loss of excitability and the creation of a transmural lesion, potentially leading to gaps, which suggests that capture loss time may not be helpful for predicting conduction gaps. On the other hand, impedance changes reflecting the delivery of electrical current to local tissues are linked to changes in tissue temperature, and seem to be useful for predicting the formation of transmural lesions. Changes in the GI have been reported as an indicator of an effective electrical delivery . A drop in the GI correlates with the lesion size, and excessive drops have been linked to steam pops. Indeed, in this study, the GI decreased throughout the ablation process. However, as shown in Table , both the value and the rate of change in the GI drop were smaller than that of the LI. Moreover, the GI is subject to variability due to factors like body weight or lung influence, presenting limitations. Conversely, the LI provides specific impedance information at the tissue‐electrode contact surface, reflecting the electrical coupling between the catheter and tissue, and correlates with the local tissue temperature. A decrease in the LI during RF energy delivery correlates more closely with the lesion size than either the force‐time index or GI drops . Given that the rate of change in the LI drop is significantly greater at any point during ablation than the decrease in the GI, the LI can offer more excellent utility for monitoring during ablation procedures than the GI.   Prediction of Ablation Gaps From the Impedance Changes Our study suggested that impedance changes were useful for predicting gaps, and compared to the GI, the LI was more sensitive to gap formation than GI. The LI obtains impedance information at the tissue‐electrode contact surface, which results in greater utility in predicting gaps than the GI. Previous reports have suggested an LI cutoff value for predicting gaps with the MiFi catheter between 12.3 and 16.1 Ω . In the present study, although a higher power setting than the previous study was applied, a similar LI cutoff value for gap prediction (15.0 Ω) was observed. On the other hand, we previously reported that the LI cutoff value for gap prediction using the StablePoint was 20.0 Ω, which was higher than that in the present study . This discrepancy might be attributed to the larger measurement distance for the LI with the STABLEPOINT (9.3 mm) as compared to the MiFi (7.5 mm), resulting in larger changes in the LI and, consequently, a higher cutoff value for the gaps in the StablePoint .   Limitations Our study had several limitations. First, due to the relatively small number of cases studied, further investigation with a larger sample size is necessary. Second, our study focused on the acute effects and did not assess outcomes during the chronic phase. The findings may differ if evaluated in the chronic phase, and the cutoff value for predicting gaps during that phase remains unclear. Third, pulse field ablation (PFA) is a new technology that has been widely adopted in catheter ablation in recent years and has the potential to become the mainstream technique for first session PVI. In PFA ablation, even reversible electroporation caused by insufficient PFA application can result in capture loss in the acute phase. Therefore, our method may only be applicable to RF ablation. Finally, the LI and the capture threshold can vary depending on the angle of the catheter, and this analysis did not take the catheter angle into consideration . The cutoff value may change depending on the catheter angle.   Conclusion The LI showed greater changes than the GI and was also useful for predicting gaps. The cutoff values of 15.0 Ω for the LI drop and −13.74% for the %LI drop could predict conduction gaps. Under the monitoring of the LI, the pacing and ablation technique proved useful for PVI, even though the MiFi catheter does not have a CF sensor or ablation indices.   H.M. and H.F. provided the study concept and design. H.M. and H.F. drafted the manuscript. K.M., M.N., T.N., W.S., N.T., and D.K. contributed to data analysis and interpretation. Y.I. and K.M. reviewed and revised the manuscript draft.   The study protocol was approved by the hospital's institutional review board (IRB number; #20‐165).   H.M. received lecture fees from Biosense Webster Japan and Boston Scientific Japan. H.F. received lecture fees from Medtronic Japan, Biosense Webster Japan, Abbott Medical Japan, and Daiichi‐Sankyo. Our department received grant support from Boston Scientific Japan and Abbott Medical Japan.   