Introduction: Acute pulmonary vein reconnection (PVR) is associated with longer procedure time and radiofrequency time during pulmonary vein isolation (PVI). However, determinants of acute PVR after high-power, short-duration PVI (HPSD-PVI) in the guidance with unipolar signal modification (USM) remain unclear. Methods and Results: We evaluated 62 patients (age, 62±12 y; 45 men) with paroxysmal atrial fibrillation undergoing USM-guided HPSD-PVI. A 50-W radiofrequency (RF) was applied for 3–5 s after unipolar signal modification. In the segments adjacent to the esophagus (SAE), RF time was limited to 5 s. Each circle was subdivided into 12 segments. For each radiofrequency tag within the circle, possible predictors of acute PVR, including minimum contact force, minimum force-time integral, minimum ablation index (AImin), minimum impedance drop (Imp-min), and maximum inter-lesion distance (ILDmax) were assessed. Acute PVR was observed in 43 (7%) SAE and 21 (17%) other segments (p = 0.001). RF energy, RF application time and bilateral isolation time were 28±8 kJ, 10±3 min, and 27±11 min, respectively. Imp-min and ILDmax had the highest area under the curve (0.69 and 0.68) and of all indices, and were the sole independent predictors of acute PVR in segments other than the SAE and SAE, respectively, after adjusting for other cofounders (odds ratio [OR]: 0.90 [0.85–0.95], p = 0.0003; and OR: 1.39 [1.11–1.74], p=0.005). Conclusions: In HPSD-PVI, a non-negligible amount of acute PVR was still observed, which was possibly dealt with an optimal target value of impedance drop and lesion distance.