Background: ‘CLOSE’-guided pulmonary vein isolation (PVI) is a point-by-point, contact force (CF)-guided radiofrequency (RF) approach aiming to enclose the PVs with contiguous RF lesions by targeting strict criteria for interlesion distance and ablation index (AI). We characterized real-time changes in bipolar (B-EGMs) and unipolar electrograms (U-EGMs) during AI-targeted RF delivery. Methods: EGM changes during 56 RF applications in 7 patients with paroxysmal atrial fibrillation (AF) undergoing ‘CLOSE’-guided PVI were studied. CF-guided RF was delivered with 35W targeting an AI of 400 at posterior and 550 at anterior wall. 336 B-EGMs and 336 U-EGMs before, during and after RF delivery were analyzed with their RF characteristics. Amplitude of the B-and U-EGM and morphology of the U-EGM were measured at each 5-second step using custom-made software. Results: We observed a significant reduction in B-EGM amplitude (0.43 [IQR=0.25, 0.55] to 0.11 [0.07, 0.22] mV, p<0.001) and U-EGM amplitude (0.57 [0.40, 0.87] to 0.22 [0.10, 0.34] mV, p<0.001) within 5 seconds, after which no more changes were observed. Impedance drop was 18.3±1.1mV. Loss of the unipolar terminal S-wave occurred in 59% of applications. There was no correlation between U-EGM morphology changes and RF characteristics. Conclusion: In AI-guided RF delivery there is a significant reduction in EGM amplitude within 5 seconds. Loss of the unipolar terminal S wave occurred in 59% of applications and was not related to RF characteristics suggestive of adequate lesion formation. These findings suggest that there is a limited value in monitoring electrograms to further optimize ‘CLOSE’-guided PVI.